diff --git a/Cargo.lock b/Cargo.lock
index 2f9aaf29541..7c5f75baecd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6071,6 +6071,7 @@ name = "mgs-dev"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "camino",
  "clap",
  "futures",
  "gateway-messages",
@@ -7680,10 +7681,12 @@ name = "omicron-dev"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "camino",
  "clap",
  "dropshot",
  "expectorate",
  "futures",
+ "gateway-test-utils",
  "libc",
  "nexus-config",
  "nexus-test-interface",
@@ -12781,6 +12784,7 @@ dependencies = [
  "gateway-types",
  "hex",
  "hubtools",
+ "nexus-types",
  "nix 0.30.1",
  "omicron-common",
  "omicron-workspace-hack",
diff --git a/dev-tools/mgs-dev/Cargo.toml b/dev-tools/mgs-dev/Cargo.toml
index 771e82a0b1c..8a38d9d26c7 100644
--- a/dev-tools/mgs-dev/Cargo.toml
+++ b/dev-tools/mgs-dev/Cargo.toml
@@ -9,6 +9,7 @@ workspace = true
 
 [dependencies]
 anyhow.workspace = true
+camino.workspace = true
 clap.workspace = true
 futures.workspace = true
 gateway-messages.workspace = true
diff --git a/dev-tools/mgs-dev/src/main.rs b/dev-tools/mgs-dev/src/main.rs
index caed71825aa..716955b6844 100644
--- a/dev-tools/mgs-dev/src/main.rs
+++ b/dev-tools/mgs-dev/src/main.rs
@@ -4,8 +4,10 @@
 
 //! Developer tool for running MGS.
 
+use camino::Utf8PathBuf;
 use clap::{Args, Parser, Subcommand};
 use futures::StreamExt;
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use libc::SIGINT;
 use signal_hook_tokio::Signals;
 use std::net::SocketAddr;
@@ -43,6 +45,9 @@ struct MgsRunArgs {
     /// Oximeter producer.
     #[clap(long)]
     nexus_address: Option<SocketAddr>,
+    /// Override the sp-sim configuration file.
+    #[clap(long, default_value = DEFAULT_SP_SIM_CONFIG)]
+    sp_sim_config_file: Utf8PathBuf,
 }
 
 impl MgsRunArgs {
@@ -54,7 +59,9 @@ impl MgsRunArgs {
 
         println!("mgs-dev: setting up MGS ... ");
         let (mut mgs_config, sp_sim_config) =
-            gateway_test_utils::setup::load_test_config();
+            gateway_test_utils::setup::load_test_config(
+                self.sp_sim_config_file.clone(),
+            );
         if let Some(addr) = self.nexus_address {
             mgs_config.metrics =
                 Some(gateway_test_utils::setup::MetricsConfig {
diff --git a/dev-tools/omicron-dev/Cargo.toml b/dev-tools/omicron-dev/Cargo.toml
index 2c7dbcabc66..17c5b89096a 100644
--- a/dev-tools/omicron-dev/Cargo.toml
+++ b/dev-tools/omicron-dev/Cargo.toml
@@ -12,9 +12,11 @@ omicron-rpaths.workspace = true
 
 [dependencies]
 anyhow.workspace = true
+camino.workspace = true
 clap.workspace = true
 dropshot.workspace = true
 futures.workspace = true
+gateway-test-utils.workspace = true
 libc.workspace = true
 nexus-config.workspace = true
 nexus-test-interface.workspace = true
diff --git a/dev-tools/omicron-dev/src/main.rs b/dev-tools/omicron-dev/src/main.rs
index 456154243d4..7eb569ba345 100644
--- a/dev-tools/omicron-dev/src/main.rs
+++ b/dev-tools/omicron-dev/src/main.rs
@@ -3,8 +3,10 @@
 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
 use anyhow::Context;
+use camino::Utf8PathBuf;
 use clap::{Args, Parser, Subcommand};
 use futures::StreamExt;
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use libc::SIGINT;
 use nexus_config::NexusConfig;
 use nexus_test_interface::NexusServer;
@@ -45,6 +47,9 @@ struct RunAllArgs {
     /// Nexus external API listen port.  Use `0` to request any available port.
     #[clap(long, action)]
     nexus_listen_port: Option<u16>,
+    /// Override the gateway server configuration file.
+    #[clap(long, default_value = DEFAULT_SP_SIM_CONFIG)]
+    gateway_config: Utf8PathBuf,
 }
 
 impl RunAllArgs {
@@ -77,7 +82,7 @@ impl RunAllArgs {
         println!("omicron-dev: setting up all services ... ");
         let cptestctx = nexus_test_utils::omicron_dev_setup_with_config::<
             omicron_nexus::Server,
-        >(&mut config, 0)
+        >(&mut config, 0, self.gateway_config.clone())
         .await
         .context("error setting up services")?;
 
diff --git a/gateway-test-utils/configs/sp_sim_config_cabooses.test.toml b/gateway-test-utils/configs/sp_sim_config_cabooses.test.toml
new file mode 100644
index 00000000000..c14316f8bd0
--- /dev/null
+++ b/gateway-test-utils/configs/sp_sim_config_cabooses.test.toml
@@ -0,0 +1,476 @@
+#
+# SP simulator: example config file with customised cabosses
+#
+
+#
+# This file contains a configuration that is different from the default
+# simulated SP configuration file by setting the values for the contents of the
+# cabooses for "SimSidecar0" and "SimGimlet00". This type of configuration file
+# is useful for cases when testing requires specific values for the cabooses.
+#
+
+#
+# NOTE: for the test suite, all ports MUST be 0 (in order to bind to any
+# available port) because the test suite will be running many servers
+# concurrently.
+#
+[[simulated_sps.sidecar]]
+serial_number = "SimSidecar0"
+manufacturing_root_cert_seed = "01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de"
+device_id_cert_seed = "01de000000000000000000000000000000000000000000000000000000000000"
+
+[simulated_sps.sidecar.cabooses.sp_slot_0]
+board = "sidecar-b"
+git_commit = "437c053649220611cdffc8a8d8d4033c0ef4b89c"
+name = "sidecar-b"
+version = "1.0.44"
+
+[simulated_sps.sidecar.cabooses.sp_slot_1]
+board = "sidecar-b"
+git_commit = "437c053649220611cdffc8a8d8d4033c0ef4b89c"
+name = "sidecar-b"
+version = "1.0.44"
+
+[simulated_sps.sidecar.cabooses.rot_slot_a]
+board = "oxide-rot-1"
+git_commit = "6edf9b5e6aa5c928a5462bda1f7a4c6f3caa40ab"
+name = "oxide-rot-1"
+version = "1.0.35"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[simulated_sps.sidecar.cabooses.rot_slot_b]
+board = "oxide-rot-1"
+git_commit = "6edf9b5e6aa5c928a5462bda1f7a4c6f3caa40ab"
+name = "oxide-rot-1"
+version = "1.0.35"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[simulated_sps.sidecar.cabooses.stage0]
+board = "oxide-rot-1"
+git_commit = "bdf56dd950b934360df596ed5b2d8b8813c92168"
+name = "oxide-rot-1"
+version = "1.4.0"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[simulated_sps.sidecar.cabooses.stage0_next]
+board = "oxide-rot-1"
+git_commit = "bdf56dd950b934360df596ed5b2d8b8813c92168"
+name = "oxide-rot-1"
+version = "1.4.0"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[[simulated_sps.sidecar.network_config]]
+[simulated_sps.sidecar.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.sidecar.network_config]]
+[simulated_sps.sidecar.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.sidecar.ereport_network_config]]
+[simulated_sps.sidecar.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.sidecar.ereport_network_config]]
+[simulated_sps.sidecar.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.sidecar.components]]
+id = "dev-0"
+device = "fake-tmp-sensor"
+description = "FAKE temperature sensor 1"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    {name = "Southwest", kind = "Temperature", last_data.value = 41.7890625, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.sidecar.components]]
+id = "dev-1"
+device = "fake-tmp-sensor"
+description = "FAKE temperature sensor 2"
+capabilities = 0x2
+presence = "Failed"
+sensors = [
+    { name = "South", kind = "Temperature", last_error.value = "DeviceError", last_error.timestamp = 1234 },
+]
+
+[simulated_sps.sidecar.ereport_config]
+restart_id = "0d3e464a-666e-4687-976f-90e31238be8b"
+
+[[simulated_sps.sidecar.ereport_config.ereports]]
+task_name = "task_thermal_server"
+task_gen = 1
+uptime = 1235
+class = "oxide.sidecar.thermal.sensor_read_error"
+sensor = { id = "dev-1", device = "fake-tmp-sensor", location = "South", presence = "Failed" }
+error = "DeviceError"
+
+[[simulated_sps.sidecar]]
+serial_number = "SimSidecar1"
+manufacturing_root_cert_seed = "01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de"
+device_id_cert_seed = "01de000000000000000000000000000000000000000000000000000000000001"
+
+[[simulated_sps.sidecar.network_config]]
+[simulated_sps.sidecar.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.sidecar.network_config]]
+[simulated_sps.sidecar.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.sidecar.ereport_network_config]]
+[simulated_sps.sidecar.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.sidecar.ereport_network_config]]
+[simulated_sps.sidecar.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet]]
+serial_number = "SimGimlet00"
+manufacturing_root_cert_seed = "01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de"
+device_id_cert_seed = "01de000000000000000000000000000000000000000000000000000000000002"
+
+[simulated_sps.gimlet.cabooses.sp_slot_0]
+board = "gimlet-e"
+git_commit = "437c053649220611cdffc8a8d8d4033c0ef4b89c"
+name = "gimlet-e"
+version = "1.0.44"
+
+[simulated_sps.gimlet.cabooses.sp_slot_1]
+board = "gimlet-e"
+git_commit = "437c053649220611cdffc8a8d8d4033c0ef4b89c"
+name = "gimlet-e"
+version = "1.0.44"
+
+[simulated_sps.gimlet.cabooses.rot_slot_a]
+board = "oxide-rot-1"
+git_commit = "6edf9b5e6aa5c928a5462bda1f7a4c6f3caa40ab"
+name = "oxide-rot-1"
+version = "1.0.35"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[simulated_sps.gimlet.cabooses.rot_slot_b]
+board = "oxide-rot-1"
+git_commit = "6edf9b5e6aa5c928a5462bda1f7a4c6f3caa40ab"
+name = "oxide-rot-1"
+version = "1.0.35"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[simulated_sps.gimlet.cabooses.stage0]
+board = "oxide-rot-1"
+git_commit = "bdf56dd950b934360df596ed5b2d8b8813c92168"
+name = "oxide-rot-1"
+version = "1.4.0"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[simulated_sps.gimlet.cabooses.stage0_next]
+board = "oxide-rot-1"
+git_commit = "bdf56dd950b934360df596ed5b2d8b8813c92168"
+name = "oxide-rot-1"
+version = "1.4.0"
+sign = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+
+[[simulated_sps.gimlet.network_config]]
+[simulated_sps.gimlet.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.network_config]]
+[simulated_sps.gimlet.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.ereport_network_config]]
+[simulated_sps.gimlet.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.ereport_network_config]]
+[simulated_sps.gimlet.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.components]]
+id = "sp3-host-cpu"
+device = "sp3-host-cpu"
+description = "FAKE host cpu"
+capabilities = 0
+presence = "Present"
+serial_console = "[::1]:0"
+
+[[simulated_sps.gimlet.components]]
+id = "dev-0"
+device = "fake-tmp-sensor"
+description = "FAKE temperature sensor"
+capabilities = 0x2
+presence = "Failed"
+sensors = [
+    { name = "Southwest", kind = "Temperature", last_error.value = "DeviceError", last_error.timestamp = 1234 },
+]
+[[simulated_sps.gimlet.components]]
+id = "dev-1"
+device = "tmp117"
+description = "FAKE temperature sensor"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "South", kind = "Temperature", last_data.value = 42.5625, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-2"
+device = "tmp117"
+description = "FAKE Southeast temperature sensor"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "Southeast", kind = "Temperature", last_data.value = 41.570313, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-6"
+device = "at24csw080"
+description = "FAKE U.2 Sharkfin A VPD"
+capabilities = 0x0
+presence = "Present"
+
+[[simulated_sps.gimlet.components]]
+id = "dev-7"
+device = "max5970"
+description = "FAKE U.2 Sharkfin A hot swap controller"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "V12_U2A_A0", kind = "Current", last_data.value = 0.45898438, last_data.timestamp = 1234 },
+    { name = "V3P3_U2A_A0", kind = "Current", last_data.value = 0.024414063, last_data.timestamp = 1234 },
+    { name = "V12_U2A_A0", kind = "Voltage", last_data.value = 12.03125, last_data.timestamp = 1234 },
+    { name = "V3P3_U2A_A0", kind = "Voltage", last_data.value = 3.328125, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-8"
+device = "nvme_bmc"
+description = "FAKE U.2 A NVMe Basic Management Command"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "U2_N0", kind = "Temperature", last_data.value = 56.0, last_data.timestamp = 1234 },
+]
+[[simulated_sps.gimlet.components]]
+id = "dev-39"
+device = "tmp451"
+description = "FAKE T6 temperature sensor"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "t6", kind = "Temperature", last_data.value = 70.625, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-46"
+device = "sbtsi"
+description = "CPU temperature sensor"
+capabilities = 2
+presence = "Present"
+sensors = [
+    { name = "CPU", kind = "Temperature", last_data.value = 64.5, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-53"
+device = "max31790"
+description = "FAKE Fan controller"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "Southeast", kind = "Speed", last_data.value = 2607.0, last_data.timestamp = 1234 },
+    { name = "Northeast", kind = "Speed", last_data.value = 2476.0, last_data.timestamp = 1234 },
+    { name = "South", kind = "Speed", last_data.value = 2553.0, last_data.timestamp = 1234 },
+    { name = "North", kind = "Speed", last_data.value = 2265.0, last_data.timestamp = 1234 },
+    { name = "Southwest", kind = "Speed", last_data.value = 2649.0, last_data.timestamp = 1234 },
+    { name = "Northwest", kind = "Speed", last_data.value = 2275.0, last_data.timestamp = 1234 },
+]
+
+[simulated_sps.gimlet.ereport_config]
+restart_id = "af1ebf85-36ba-4c31-bbec-b9825d6d9d8b"
+
+[[simulated_sps.gimlet.ereport_config.ereports]]
+task_name = "task_apollo_server"
+task_gen = 13
+uptime = 1233
+class = "gov.nasa.apollo.o2_tanks.stir.begin"
+message = "stirring the tanks"
+
+[[simulated_sps.gimlet.ereport_config.ereports]]
+task_name = "drv_ae35_server"
+task_gen = 1
+uptime = 1234
+class = "io.discovery.ae35.fault"
+message = "i've just picked up a fault in the AE-35 unit"
+de = { scheme = "fmd", authority = { product-id = "HAL-9000-series computer", server-id = "HAL 9000"}, mod-name = "ae35-diagnosis" }
+hours_to_failure = 72
+
+[[simulated_sps.gimlet.ereport_config.ereports]]
+task_name = "task_apollo_server"
+task_gen = 13
+uptime = 1237
+class = "gov.nasa.apollo.fault"
+message = "houston, we have a problem"
+crew = ["Lovell", "Swigert", "Haise"]
+
+[[simulated_sps.gimlet.ereport_config.ereports]]
+task_name = "drv_thingy_server"
+task_gen = 2
+uptime = 1240
+class = "flagrant_error"
+computer = false
+
+[[simulated_sps.gimlet.ereport_config.ereports]]
+task_name = "task_latex_server"
+task_gen = 1
+uptime = 1245
+class = "overfull_hbox"
+badness  = 10000
+
+[[simulated_sps.gimlet]]
+serial_number = "SimGimlet01"
+manufacturing_root_cert_seed = "01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de01de"
+device_id_cert_seed = "01de000000000000000000000000000000000000000000000000000000000003"
+
+[[simulated_sps.gimlet.network_config]]
+[simulated_sps.gimlet.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.network_config]]
+[simulated_sps.gimlet.network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.ereport_network_config]]
+[simulated_sps.gimlet.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.ereport_network_config]]
+[simulated_sps.gimlet.ereport_network_config.simulated]
+bind_addr = "[::1]:0"
+
+[[simulated_sps.gimlet.components]]
+id = "sp3-host-cpu"
+device = "sp3-host-cpu"
+description = "FAKE host cpu"
+capabilities = 0
+presence = "Present"
+serial_console = "[::1]:0"
+
+
+[[simulated_sps.gimlet.components]]
+id = "dev-0"
+device = "tmp117"
+description = "FAKE temperature sensor"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "Southwest", kind = "Temperature", last_data.value = 41.3629, last_data.timestamp = 1234 },
+]
+[[simulated_sps.gimlet.components]]
+id = "dev-1"
+device = "tmp117"
+description = "FAKE temperature sensor"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "South", kind = "Temperature", last_data.value = 42.5625, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-2"
+device = "tmp117"
+description = "FAKE Southeast temperature sensor"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "Southeast", kind = "Temperature", last_data.value = 41.570313, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-6"
+device = "at24csw080"
+description = "FAKE U.2 Sharkfin A VPD"
+capabilities = 0x0
+presence = "Present"
+
+[[simulated_sps.gimlet.components]]
+id = "dev-7"
+device = "max5970"
+description = "FAKE U.2 Sharkfin A hot swap controller"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "V12_U2A_A0", kind = "Current", last_data.value = 0.41893438, last_data.timestamp = 1234 },
+    { name = "V3P3_U2A_A0", kind = "Current", last_data.value = 0.025614603, last_data.timestamp = 1234 },
+    { name = "V12_U2A_A0", kind = "Voltage", last_data.value = 12.02914, last_data.timestamp = 1234 },
+    { name = "V3P3_U2A_A0", kind = "Voltage", last_data.value = 3.2618, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-8"
+device = "nvme_bmc"
+description = "FAKE U.2 A NVMe Basic Management Command"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "U2_N0", kind = "Temperature", last_data.value = 56.0, last_data.timestamp = 1234 },
+]
+[[simulated_sps.gimlet.components]]
+id = "dev-39"
+device = "tmp451"
+description = "FAKE T6 temperature sensor"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "t6", kind = "Temperature", last_data.value = 70.625, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-46"
+device = "sbtsi"
+description = "CPU temperature sensor"
+capabilities = 2
+presence = "Present"
+sensors = [
+    { name = "CPU", kind = "Temperature", last_data.value = 62.6, last_data.timestamp = 1234 },
+]
+
+[[simulated_sps.gimlet.components]]
+id = "dev-53"
+device = "max31790"
+description = "FAKE Fan controller"
+capabilities = 0x2
+presence = "Present"
+sensors = [
+    { name = "Southeast", kind = "Speed", last_data.value = 2510.0, last_data.timestamp = 1234 },
+    { name = "Northeast", kind = "Speed", last_data.value = 2390.0, last_data.timestamp = 1234 },
+    { name = "South", kind = "Speed", last_data.value = 2467.0, last_data.timestamp = 1234 },
+    { name = "North", kind = "Speed", last_data.value = 2195.0, last_data.timestamp = 1234 },
+    { name = "Southwest", kind = "Speed", last_data.value = 2680.0, last_data.timestamp = 1234 },
+    { name = "Northwest", kind = "Speed", last_data.value = 2212.0, last_data.timestamp = 1234 },
+]
+
+[simulated_sps.gimlet.ereport_config]
+restart_id = "55e30cc7-a109-492f-aca9-735ed725df3c"
+
+[[simulated_sps.gimlet.ereport_config.ereports]]
+task_name = "task_thermal_server"
+task_gen = 1
+uptime = 1233
+class = "computer.oxide.gimlet.chassis_integrity.fault"
+nosub_class = "chassis_integrity.cat_hair_detected"
+message = "cat hair detected inside gimlet"
+de = { scheme = "fmd", mod-name = "hubris-thermal-diagnosis", mod-version = "1.0", authority = { "product-id" = "oxide", server-id = "SimGimlet1" }}
+certainty = 0x64
+cat_hair_amount = 10000
+
+#
+# NOTE: for the test suite, the [log] section is ignored; sp-sim logs are rolled
+# into the gateway logfile.
+#
+[log]
+level = "debug"
+mode = "stderr-terminal"
diff --git a/gateway-test-utils/src/setup.rs b/gateway-test-utils/src/setup.rs
index dea606ab77c..fd5dbd29211 100644
--- a/gateway-test-utils/src/setup.rs
+++ b/gateway-test-utils/src/setup.rs
@@ -5,6 +5,7 @@
 // Copyright 2022 Oxide Computer Company
 
 use camino::Utf8Path;
+use camino::Utf8PathBuf;
 use dropshot::test_util::ClientTestContext;
 use dropshot::test_util::LogContext;
 use gateway_messages::SpPort;
@@ -32,6 +33,8 @@ use uuid::Uuid;
 // TODO this exact value is copy/pasted from `nexus/test-utils` - should we
 // import it or have our own?
 const RACK_UUID: &str = "c19a698f-c6f9-4a17-ae30-20d711b8f7dc";
+pub const DEFAULT_SP_SIM_CONFIG: &str =
+    concat!(env!("CARGO_MANIFEST_DIR"), "/configs/sp_sim_config.test.toml");
 
 pub struct GatewayTestContext {
     pub client: ClientTestContext,
@@ -62,24 +65,22 @@ impl GatewayTestContext {
     }
 }
 
-pub fn load_test_config() -> (omicron_gateway::Config, sp_sim::Config) {
+pub fn load_test_config(
+    sp_sim_config_file: Utf8PathBuf,
+) -> (omicron_gateway::Config, sp_sim::Config) {
     // The test configs are located relative to the directory this file is in.
     // TODO: embed these with include_str! instead?
     let manifest_dir = Utf8Path::new(env!("CARGO_MANIFEST_DIR"));
-    let server_config_file_path = manifest_dir.join("configs/config.test.toml");
-    let server_config =
-        match omicron_gateway::Config::from_file(&server_config_file_path) {
-            Ok(config) => config,
-            Err(e) => panic!("failed to load MGS config: {e}"),
-        };
+    let config_path = manifest_dir.join("configs/config.test.toml");
+    let server_config = omicron_gateway::Config::from_file(&config_path)
+        .unwrap_or_else(|e| {
+            panic!("failed to load MGS config from {config_path}: {e}")
+        });
 
-    let sp_sim_config_file_path =
-        manifest_dir.join("configs/sp_sim_config.test.toml");
-    let sp_sim_config =
-        match sp_sim::Config::from_file(&sp_sim_config_file_path) {
-            Ok(config) => config,
-            Err(e) => panic!("failed to load SP simulator config: {e}"),
-        };
+    let sp_sim_config = match sp_sim::Config::from_file(sp_sim_config_file) {
+        Ok(config) => config,
+        Err(e) => panic!("failed to load SP simulator config: {e}"),
+    };
     (server_config, sp_sim_config)
 }
 
@@ -87,7 +88,8 @@ pub async fn test_setup(
     test_name: &str,
     sp_port: SpPort,
 ) -> GatewayTestContext {
-    let (server_config, sp_sim_config) = load_test_config();
+    let (server_config, sp_sim_config) =
+        load_test_config(DEFAULT_SP_SIM_CONFIG.into());
     test_setup_with_config(
         test_name,
         sp_port,
diff --git a/nexus/mgs-updates/tests/sp_updater.rs b/nexus/mgs-updates/tests/sp_updater.rs
index ef7c4cd7978..bae4d1eaa9d 100644
--- a/nexus/mgs-updates/tests/sp_updater.rs
+++ b/nexus/mgs-updates/tests/sp_updater.rs
@@ -7,7 +7,7 @@
 use gateway_client::SpComponent;
 use gateway_client::types::SpType;
 use gateway_messages::{SpPort, UpdateInProgressStatus, UpdateStatus};
-use gateway_test_utils::setup as mgs_setup;
+use gateway_test_utils::setup::{self as mgs_setup, DEFAULT_SP_SIM_CONFIG};
 use hubtools::RawHubrisArchive;
 use hubtools::{CabooseBuilder, HubrisArchiveBuilder};
 use nexus_mgs_updates::{MgsClients, SpUpdater, UpdateProgress};
@@ -567,7 +567,8 @@ async fn test_sp_updater_switches_mgs_instances_on_failure() {
 async fn test_sp_updater_delivers_progress() {
     // Start MGS + Sim SP.
     let mgstestctx = {
-        let (mut mgs_config, sp_sim_config) = mgs_setup::load_test_config();
+        let (mut mgs_config, sp_sim_config) =
+            mgs_setup::load_test_config(DEFAULT_SP_SIM_CONFIG.into());
         // Enabling SP metrics collection makes this alread-flaky test even
         // flakier, so let's just turn it off.
         // TODO(eliza): it would be nice if we didn't have to disable metrics in
diff --git a/nexus/test-utils/src/lib.rs b/nexus/test-utils/src/lib.rs
index 9a76249fb12..e5aaf2474d4 100644
--- a/nexus/test-utils/src/lib.rs
+++ b/nexus/test-utils/src/lib.rs
@@ -8,6 +8,7 @@
 use anyhow::Context;
 use anyhow::Result;
 use camino::Utf8Path;
+use camino::Utf8PathBuf;
 use chrono::Utc;
 use dropshot::ConfigLogging;
 use dropshot::ConfigLoggingLevel;
@@ -16,6 +17,7 @@ use dropshot::test_util::ClientTestContext;
 use dropshot::test_util::LogContext;
 use futures::FutureExt;
 use futures::future::BoxFuture;
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use gateway_test_utils::setup::GatewayTestContext;
 use hickory_resolver::TokioResolver;
 use hickory_resolver::config::NameServerConfig;
@@ -327,6 +329,7 @@ pub async fn test_setup<N: NexusServer>(
         sim::SimMode::Explicit,
         None,
         extra_sled_agents,
+        DEFAULT_SP_SIM_CONFIG.into(),
     )
     .await
 }
@@ -673,10 +676,12 @@ impl<'a, N: NexusServer> ControlPlaneTestContextBuilder<'a, N> {
         &mut self,
         switch_location: SwitchLocation,
         port: Option<u16>,
+        sp_sim_config_file: Utf8PathBuf,
     ) {
         debug!(&self.logctx.log, "Starting Management Gateway");
         let (mgs_config, sp_sim_config) =
-            gateway_test_utils::setup::load_test_config();
+            gateway_test_utils::setup::load_test_config(sp_sim_config_file);
+
         let mgs_addr =
             port.map(|port| SocketAddrV6::new(Ipv6Addr::LOCALHOST, port, 0, 0));
         let gateway = gateway_test_utils::setup::test_setup_with_config(
@@ -1583,6 +1588,7 @@ enum PopulateCrdb {
 pub async fn omicron_dev_setup_with_config<N: NexusServer>(
     config: &mut NexusConfig,
     extra_sled_agents: u16,
+    gateway_config_file: Utf8PathBuf,
 ) -> Result<ControlPlaneTestContext<N>> {
     let builder =
         ControlPlaneTestContextBuilder::<N>::new("omicron-dev", config);
@@ -1609,6 +1615,7 @@ pub async fn omicron_dev_setup_with_config<N: NexusServer>(
         sim::SimMode::Auto,
         None,
         extra_sled_agents,
+        gateway_config_file,
     )
     .await)
 }
@@ -1620,6 +1627,7 @@ pub async fn test_setup_with_config<N: NexusServer>(
     sim_mode: sim::SimMode,
     initial_cert: Option<Certificate>,
     extra_sled_agents: u16,
+    gateway_config_file: Utf8PathBuf,
 ) -> ControlPlaneTestContext<N> {
     let builder = ControlPlaneTestContextBuilder::<N>::new(test_name, config);
     setup_with_config_impl(
@@ -1628,6 +1636,7 @@ pub async fn test_setup_with_config<N: NexusServer>(
         sim_mode,
         initial_cert,
         extra_sled_agents,
+        gateway_config_file,
     )
     .await
 }
@@ -1638,6 +1647,7 @@ async fn setup_with_config_impl<N: NexusServer>(
     sim_mode: sim::SimMode,
     initial_cert: Option<Certificate>,
     extra_sled_agents: u16,
+    gateway_config_file: Utf8PathBuf,
 ) -> ControlPlaneTestContext<N> {
     const STEP_TIMEOUT: Duration = Duration::from_secs(60);
 
@@ -1664,6 +1674,7 @@ async fn setup_with_config_impl<N: NexusServer>(
     // be configured. If extra sled agents are requested, then the second sled
     // agent will be for switch1.
 
+    let mgs_config = gateway_config_file.clone();
     builder
         .init_with_steps(
             vec![
@@ -1671,7 +1682,11 @@ async fn setup_with_config_impl<N: NexusServer>(
                     "start_gateway_switch0",
                     Box::new(|builder| {
                         builder
-                            .start_gateway(SwitchLocation::Switch0, None)
+                            .start_gateway(
+                                SwitchLocation::Switch0,
+                                None,
+                                mgs_config,
+                            )
                             .boxed()
                     }),
                 ),
@@ -1711,7 +1726,11 @@ async fn setup_with_config_impl<N: NexusServer>(
                         "start_gateway_switch1",
                         Box::new(|builder| {
                             builder
-                                .start_gateway(SwitchLocation::Switch1, None)
+                                .start_gateway(
+                                    SwitchLocation::Switch1,
+                                    None,
+                                    gateway_config_file,
+                                )
                                 .boxed()
                         }),
                     ),
diff --git a/nexus/tests/integration_tests/certificates.rs b/nexus/tests/integration_tests/certificates.rs
index 57d90e27006..79711ea1995 100644
--- a/nexus/tests/integration_tests/certificates.rs
+++ b/nexus/tests/integration_tests/certificates.rs
@@ -8,6 +8,7 @@ use display_error_chain::ErrorChainExt;
 use dropshot::HttpErrorResponseBody;
 use dropshot::test_util::ClientTestContext;
 use futures::TryStreamExt;
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use http::StatusCode;
 use http::method::Method;
 use internal_dns_types::names::DNS_ZONE_EXTERNAL_TESTING;
@@ -351,6 +352,7 @@ async fn test_silo_certificates() {
             omicron_sled_agent::sim::SimMode::Explicit,
             Some(silo1.cert.clone()),
             0,
+            DEFAULT_SP_SIM_CONFIG.into(),
         )
         .await
     };
diff --git a/nexus/tests/integration_tests/console_api.rs b/nexus/tests/integration_tests/console_api.rs
index 8609474e212..f3cadbe9e9a 100644
--- a/nexus/tests/integration_tests/console_api.rs
+++ b/nexus/tests/integration_tests/console_api.rs
@@ -6,6 +6,7 @@ use anyhow::Context;
 use camino::Utf8PathBuf;
 use dropshot::ResultsPage;
 use dropshot::test_util::ClientTestContext;
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use http::{StatusCode, header, method::Method};
 use nexus_auth::context::OpContext;
 use std::env::current_dir;
@@ -393,6 +394,7 @@ async fn test_absolute_static_dir() {
         sim::SimMode::Explicit,
         None,
         0,
+        DEFAULT_SP_SIM_CONFIG.into(),
     )
     .await;
     let testctx = &cptestctx.external_client;
@@ -903,6 +905,7 @@ async fn test_session_idle_timeout_deletes_session() {
         sim::SimMode::Explicit,
         None,
         0,
+        DEFAULT_SP_SIM_CONFIG.into(),
     )
     .await;
     let testctx = &cptestctx.external_client;
diff --git a/nexus/tests/integration_tests/device_auth.rs b/nexus/tests/integration_tests/device_auth.rs
index 60532eff4e8..78ea189a629 100644
--- a/nexus/tests/integration_tests/device_auth.rs
+++ b/nexus/tests/integration_tests/device_auth.rs
@@ -7,6 +7,7 @@ use std::num::NonZeroU32;
 use chrono::Utc;
 use dropshot::test_util::ClientTestContext;
 use dropshot::{HttpErrorResponseBody, ResultsPage};
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use nexus_auth::authn::USER_TEST_UNPRIVILEGED;
 use nexus_config::NexusConfig;
 use nexus_db_queries::db::fixed_data::silo::DEFAULT_SILO;
@@ -803,6 +804,7 @@ async fn test_session_list_with_config(
         sim::SimMode::Explicit,
         None,
         0,
+        DEFAULT_SP_SIM_CONFIG.into(),
     )
     .await;
     let testctx = &cptestctx.external_client;
diff --git a/nexus/tests/integration_tests/initialization.rs b/nexus/tests/integration_tests/initialization.rs
index 989029625a5..fa4511d6de1 100644
--- a/nexus/tests/integration_tests/initialization.rs
+++ b/nexus/tests/integration_tests/initialization.rs
@@ -2,6 +2,7 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use nexus_config::Database;
 use nexus_config::InternalDns;
 use nexus_test_interface::NexusServer;
@@ -90,8 +91,20 @@ async fn test_nexus_boots_before_dendrite() {
     // inside of Nexus initialization.  We must use MGS_PORT here because Nexus
     // hardcodes it.
     info!(&log, "Starting MGS");
-    builder.start_gateway(SwitchLocation::Switch0, Some(MGS_PORT)).await;
-    builder.start_gateway(SwitchLocation::Switch1, None).await;
+    builder
+        .start_gateway(
+            SwitchLocation::Switch0,
+            Some(MGS_PORT),
+            DEFAULT_SP_SIM_CONFIG.into(),
+        )
+        .await;
+    builder
+        .start_gateway(
+            SwitchLocation::Switch1,
+            None,
+            DEFAULT_SP_SIM_CONFIG.into(),
+        )
+        .await;
     info!(&log, "Started MGS");
 
     let populate = true;
diff --git a/nexus/tests/integration_tests/metrics.rs b/nexus/tests/integration_tests/metrics.rs
index 7b36814cbc6..bf3551353e6 100644
--- a/nexus/tests/integration_tests/metrics.rs
+++ b/nexus/tests/integration_tests/metrics.rs
@@ -9,6 +9,7 @@ use crate::integration_tests::instances::{
 };
 use chrono::Utc;
 use dropshot::HttpErrorResponseBody;
+use gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG;
 use http::{Method, StatusCode};
 use nexus_auth::authn::USER_TEST_UNPRIVILEGED;
 use nexus_db_queries::db::identity::Asset;
@@ -651,7 +652,9 @@ async fn test_mgs_metrics(
 ) {
     // Make a MGS
     let (mut mgs_config, sp_sim_config) =
-        gateway_test_utils::setup::load_test_config();
+        gateway_test_utils::setup::load_test_config(
+            DEFAULT_SP_SIM_CONFIG.into(),
+        );
     let mgs = {
         // munge the already-parsed MGS config file to point it at the test
         // Nexus' address.
diff --git a/sp-sim/Cargo.toml b/sp-sim/Cargo.toml
index 9f273d4ac69..0f453d416c8 100644
--- a/sp-sim/Cargo.toml
+++ b/sp-sim/Cargo.toml
@@ -18,6 +18,7 @@ gateway-messages.workspace = true
 gateway-types.workspace = true
 hex = { workspace = true, features = [ "serde" ] }
 hubtools.workspace = true
+nexus-types.workspace = true
 omicron-common.workspace = true
 oxide-tokio-rt.workspace = true
 serde.workspace = true
diff --git a/sp-sim/src/config.rs b/sp-sim/src/config.rs
index b78d0ab58fa..d5c03d87b7c 100644
--- a/sp-sim/src/config.rs
+++ b/sp-sim/src/config.rs
@@ -9,6 +9,7 @@ use crate::sensors;
 use dropshot::ConfigLogging;
 use gateway_messages::DeviceCapabilities;
 use gateway_messages::DevicePresence;
+use nexus_types::inventory::Caboose;
 use serde::Deserialize;
 use serde::Serialize;
 use std::net::Ipv6Addr;
@@ -70,6 +71,17 @@ impl slog::KV for NetworkConfig {
     }
 }
 
+/// Configuration for every caboose in the SP
+#[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
+pub struct SpCabooses {
+    pub sp_slot_0: Caboose,
+    pub sp_slot_1: Caboose,
+    pub rot_slot_a: Caboose,
+    pub rot_slot_b: Caboose,
+    pub stage0: Caboose,
+    pub stage0_next: Caboose,
+}
+
 /// Common configuration for all flavors of SP
 #[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
 pub struct SpCommonConfig {
@@ -100,6 +112,10 @@ pub struct SpCommonConfig {
     /// Fake ereport configuration
     #[serde(default)]
     pub ereport_config: EreportConfig,
+    /// Configurable caboose values. If unset, these will be
+    /// populated with default values
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cabooses: Option<SpCabooses>,
 }
 
 /// Configuration of a simulated SP component
diff --git a/sp-sim/src/gimlet.rs b/sp-sim/src/gimlet.rs
index 4250b4a7aed..c6daf61f7d6 100644
--- a/sp-sim/src/gimlet.rs
+++ b/sp-sim/src/gimlet.rs
@@ -296,6 +296,7 @@ impl Gimlet {
             BaseboardKind::Gimlet,
             gimlet.common.no_stage0_caboose,
             phase1_hash_policy,
+            gimlet.common.cabooses.clone(),
         );
         let ereport_state = {
             let mut cfg = gimlet.common.ereport_config.clone();
diff --git a/sp-sim/src/sidecar.rs b/sp-sim/src/sidecar.rs
index 341cc0994de..828049b8807 100644
--- a/sp-sim/src/sidecar.rs
+++ b/sp-sim/src/sidecar.rs
@@ -255,6 +255,14 @@ impl Sidecar {
                 EreportState::new(cfg, ereport_log)
             };
 
+            let update_state = SimSpUpdate::new(
+                BaseboardKind::Sidecar,
+                sidecar.common.no_stage0_caboose,
+                // sidecar doesn't have phase 1 flash; any policy is fine
+                HostFlashHashPolicy::assume_already_hashed(),
+                sidecar.common.cabooses.clone(),
+            );
+
             let power_state_changes = Arc::new(AtomicUsize::new(0));
             let (inner, handler, responses_sent_count) = Inner::new(
                 servers,
@@ -266,7 +274,7 @@ impl Sidecar {
                 commands_rx,
                 log,
                 sidecar.common.old_rot_state,
-                sidecar.common.no_stage0_caboose,
+                update_state,
                 Arc::clone(&power_state_changes),
             );
             let inner_task =
@@ -338,7 +346,7 @@ impl Inner {
         commands: mpsc::UnboundedReceiver<Command>,
         log: Logger,
         old_rot_state: bool,
-        no_stage0_caboose: bool,
+        update_state: SimSpUpdate,
         power_state_changes: Arc<AtomicUsize>,
     ) -> (Self, Arc<TokioMutex<Handler>>, watch::Receiver<usize>) {
         let [udp0, udp1] = servers;
@@ -348,7 +356,7 @@ impl Inner {
             ignition,
             log,
             old_rot_state,
-            no_stage0_caboose,
+            update_state,
             power_state_changes,
         )));
         let responses_sent_count = watch::Sender::new(0);
@@ -513,7 +521,7 @@ impl Handler {
         ignition: FakeIgnition,
         log: Logger,
         old_rot_state: bool,
-        no_stage0_caboose: bool,
+        update_state: SimSpUpdate,
         power_state_changes: Arc<AtomicUsize>,
     ) -> Self {
         let mut leaked_component_device_strings =
@@ -542,12 +550,7 @@ impl Handler {
             ignition,
             power_state: PowerState::A2,
             power_state_changes,
-            update_state: SimSpUpdate::new(
-                BaseboardKind::Sidecar,
-                no_stage0_caboose,
-                // sidecar doesn't have phase 1 flash; any policy is fine
-                HostFlashHashPolicy::assume_already_hashed(),
-            ),
+            update_state,
             reset_pending: None,
             should_fail_to_respond_signal: None,
             old_rot_state,
diff --git a/sp-sim/src/update.rs b/sp-sim/src/update.rs
index 35e54e9d162..6defb14b8b4 100644
--- a/sp-sim/src/update.rs
+++ b/sp-sim/src/update.rs
@@ -12,6 +12,7 @@ use crate::SIM_GIMLET_BOARD;
 use crate::SIM_ROT_BOARD;
 use crate::SIM_ROT_STAGE0_BOARD;
 use crate::SIM_SIDECAR_BOARD;
+use crate::config::SpCabooses;
 use crate::helpers::rot_slot_id_from_u16;
 use crate::helpers::rot_slot_id_to_u16;
 use gateway_messages::Fwid;
@@ -24,6 +25,7 @@ use gateway_messages::UpdateChunk;
 use gateway_messages::UpdateId;
 use gateway_messages::UpdateInProgressStatus;
 use hubtools::RawHubrisImage;
+use nexus_types::inventory::Caboose;
 use omicron_common::disk::M2Slot;
 use sha2::Sha256;
 use sha3::Digest;
@@ -78,6 +80,7 @@ impl SimSpUpdate {
         baseboard_kind: BaseboardKind,
         no_stage0_caboose: bool,
         phase1_hash_policy: HostFlashHashPolicy,
+        cabooses: Option<SpCabooses>,
     ) -> Self {
         const SP_GITC0: &str = "ffffffff";
         const SP_GITC1: &str = "fefefefe";
@@ -97,46 +100,78 @@ impl SimSpUpdate {
         const STAGE0_VERS0: &str = "0.0.200";
         const STAGE0_VERS1: &str = "0.0.200";
 
-        let sp_board = baseboard_kind.sp_board();
-        let sp_name = baseboard_kind.sp_name();
-        let rot_name = baseboard_kind.rot_name();
-
-        let caboose_sp_active = CabooseValue::Caboose(
-            hubtools::CabooseBuilder::default()
-                .git_commit(SP_GITC0)
-                .board(sp_board)
-                .name(sp_name)
-                .version(SP_VERS0)
-                .build(),
-        );
-        let caboose_sp_inactive = CabooseValue::Caboose(
-            hubtools::CabooseBuilder::default()
-                .git_commit(SP_GITC1)
-                .board(sp_board)
-                .name(sp_name)
-                .version(SP_VERS1)
-                .build(),
-        );
-
-        let caboose_rot_a = CabooseValue::Caboose(
-            hubtools::CabooseBuilder::default()
-                .git_commit(ROT_GITC0)
-                .board(SIM_ROT_BOARD)
-                .name(rot_name)
-                .version(ROT_VERS0)
-                .sign(ROT_STAGING_DEVEL_SIGN)
-                .build(),
-        );
-
-        let caboose_rot_b = CabooseValue::Caboose(
-            hubtools::CabooseBuilder::default()
-                .git_commit(ROT_GITC1)
-                .board(SIM_ROT_BOARD)
-                .name(rot_name)
-                .version(ROT_VERS1)
-                .sign(ROT_STAGING_DEVEL_SIGN)
-                .build(),
-        );
+        // If we find in the config preset cabooses we use those. Otherwise, we
+        // can use default values
+        let (
+            sp_active_src,
+            sp_inactive_src,
+            rot_a_src,
+            rot_b_src,
+            stage0_src,
+            stage0_next_src,
+        ) = if let Some(c) = cabooses {
+            (
+                c.sp_slot_0,
+                c.sp_slot_1,
+                c.rot_slot_a,
+                c.rot_slot_b,
+                c.stage0,
+                c.stage0_next,
+            )
+        } else {
+            let sp_board = baseboard_kind.sp_board().to_string();
+            let sp_name = baseboard_kind.sp_name().to_string();
+            let rot_name = baseboard_kind.rot_name().to_string();
+            (
+                Caboose {
+                    git_commit: SP_GITC0.to_string(),
+                    board: sp_board.clone(),
+                    name: sp_name.clone(),
+                    version: SP_VERS0.to_string(),
+                    sign: None,
+                },
+                Caboose {
+                    git_commit: SP_GITC1.to_string(),
+                    board: sp_board.clone(),
+                    name: sp_name.clone(),
+                    version: SP_VERS1.to_string(),
+                    sign: None,
+                },
+                Caboose {
+                    git_commit: ROT_GITC0.to_string(),
+                    board: SIM_ROT_BOARD.to_string(),
+                    name: rot_name.clone(),
+                    version: ROT_VERS0.to_string(),
+                    sign: Some(ROT_STAGING_DEVEL_SIGN.to_string()),
+                },
+                Caboose {
+                    git_commit: ROT_GITC1.to_string(),
+                    board: SIM_ROT_BOARD.to_string(),
+                    name: rot_name.clone(),
+                    version: ROT_VERS1.to_string(),
+                    sign: Some(ROT_STAGING_DEVEL_SIGN.to_string()),
+                },
+                Caboose {
+                    git_commit: STAGE0_GITC0.to_string(),
+                    board: SIM_ROT_STAGE0_BOARD.to_string(),
+                    name: rot_name.clone(),
+                    version: STAGE0_VERS0.to_string(),
+                    sign: Some(ROT_STAGING_DEVEL_SIGN.to_string()),
+                },
+                Caboose {
+                    git_commit: STAGE0_GITC1.to_string(),
+                    board: SIM_ROT_STAGE0_BOARD.to_string(),
+                    name: rot_name.clone(),
+                    version: STAGE0_VERS1.to_string(),
+                    sign: Some(ROT_STAGING_DEVEL_SIGN.to_string()),
+                },
+            )
+        };
+
+        let caboose_sp_active = build_caboose(sp_active_src);
+        let caboose_sp_inactive = build_caboose(sp_inactive_src);
+        let caboose_rot_a = build_caboose(rot_a_src);
+        let caboose_rot_b = build_caboose(rot_b_src);
 
         let (caboose_stage0, caboose_stage0next) = if no_stage0_caboose {
             (
@@ -144,26 +179,7 @@ impl SimSpUpdate {
                 CabooseValue::InvalidMissingAllKeys,
             )
         } else {
-            (
-                CabooseValue::Caboose(
-                    hubtools::CabooseBuilder::default()
-                        .git_commit(STAGE0_GITC0)
-                        .board(SIM_ROT_STAGE0_BOARD)
-                        .name(rot_name)
-                        .version(STAGE0_VERS0)
-                        .sign(ROT_STAGING_DEVEL_SIGN)
-                        .build(),
-                ),
-                CabooseValue::Caboose(
-                    hubtools::CabooseBuilder::default()
-                        .git_commit(STAGE0_GITC1)
-                        .board(SIM_ROT_STAGE0_BOARD)
-                        .name(rot_name)
-                        .version(STAGE0_VERS1)
-                        .sign(ROT_STAGING_DEVEL_SIGN)
-                        .build(),
-                ),
-            )
+            (build_caboose(stage0_src), build_caboose(stage0_next_src))
         };
 
         const SLOT_A_DIGEST: [u8; 32] = [0xaa; 32];
@@ -750,6 +766,21 @@ impl CabooseValue {
     }
 }
 
+// A helper function to build a CabooseValue from Caboose
+fn build_caboose(source: Caboose) -> CabooseValue {
+    let mut builder = hubtools::CabooseBuilder::default()
+        .git_commit(source.git_commit)
+        .board(source.board)
+        .name(source.name)
+        .version(source.version);
+
+    if let Some(sign_str) = source.sign {
+        builder = builder.sign(sign_str);
+    }
+
+    CabooseValue::Caboose(builder.build())
+}
+
 enum UpdateState {
     NotPrepared,
     Prepared {