I haven't taken my Cargo heater apart but notice there are several wires to the heater. Is the thermostat inside the heater? When turning on the heater from inside the coach the heater is supposed to automatically turn on at 35 and off at 45 degrees. I think any 12 volt heater would work if it was no more than 300 watts. Doesn't Monaco stock the Cargo heater? I have a Cargo heater in my 2013 Monaco.
I only have had opportunity to check my heater once when I was in 10 degree wx. Last night it was 29 but wet bay was still at 42 degrees so heater never turned on.