CAM_DURATION = 1
CAM_TRIGG_TYPE = 1 (Relay)
RC13_FUNCTION = 10 (camera_trigger)
RELAY_PIN = 54 (Pixhawk AUXOUT5)
To test set CH7_OPT = 9 (Camera Trigger)
*Note - if you go to the INITIAL SETUP>Camera Gimbal screen it sets CAM_TRIGG_TYPE to 0 (Servo), so you need to go back to the Full Parameter List and set it back to relay.
Oops!.. should have probably posted this in the Pixhawk Family group.
Thanks for putting this where it belongs Naterater.