I need to check this but I think my Ford truck drops the aux 12V power when the engine is off so the fridge will not discharge the battery while stopped.

The trailer must be "up" to run the fridge on propane safely per the factory.

One more thing David, I bought mine used to save some $s.
I suspect you will have one before too long.

Sure enjoy mine and that is after owning a Class A Motorhome for 10 +/- years.