B+ motorhomes

TonyTiger - Welcome back to this thread. A GFI tripping does not usually mean overcurrent rather it typically means a short (internally to the device) to ground. Having the fridge on auto sets the fridge to automatically switch to gas if no 120V AC power is available or vice versa. Does the GFI trip immediately when the fridge goes to 120V AC? I believe you are saying, the GFI never trips if the fridge is either turned off or set to propane only; is that correct? If that is true, it is the fridge causing the problem and not some other device that might co-incidentally turn on and pull power (i.e. the steps). I would try plugging the fridge into a long extension cord to the barn GFI and see if it trips the circuit just to be sure it is the fridge. I would also try plugging that same long extension cord to the barn in a non-GFI receptacle just to be sure the fridge is not drawing too much current. If the fridge does not trip a non-GFI receptacle it likely will run fine on 120V AC from generator power or shore power that does not have GFI protection. However, if you happen to touch the chassis of the fridge with one hand and a good ground with the other hand you'll feel the tingling or worse - not safe.

You should be able to take an "ohm" meter and after unplugging the fridge from the 120V receptacle get a resistance of something other than "1" between the round pin and either of the flat pins on the power plug of the fridge.

After all of the above, I would suspect you have a simple short in the electric heater on your fridge.