Puzzling electrical problem in 5’er

[harris71]

I’ll preface this with my knowledge level of electrical is advanced, but not quite electrician caliber. I brought my 2013 3100RL home from the storage lot to do some maintenance this week. I plugged it in to a receptacle in my garage using the 50 to 30 pigtail and a 30 to 15 adapter (as has been done many times before, as recently as November). Lights inside worked fine but when I brought my shopvac in to do some cleaning, I plugged it into one of the camper’s 110v receptacles and it tripped the garage GFCI (not the circuit breaker). I reset it, tried again and the same result. Tried a different receptacle in the camper; tripped also. Plugging the shopvac directly into said garage GFCI and it worked fine. I tested voltage in the camper receptacles with a multi-meter and wiring with a 3 prong analyzer and everything reads fine. The TV in the rig came on and works, as did the microwave. I plugged in a 2 amp battery charger and it worked OK. Then tried a hair dryer, it worked. Turned on the fridge (RV type, not residential) and the GFCI tripped. I tried another GFCI (fairly new) on a different circuit and it also tripped, so it’s not the GFCI receptacle.

Online searches indicate a GFCI can also trip under load, which leaves me to believe there is some small to medium call for a/c current from the RV that is new (a minor short?). I took the cover off the breaker panel and checked for loose connections. I searched under the kitchen sink, front and side storage compartments for any evidence of critters….. nothing.

I’m tossing it out to the Forum for any insight/assistance. I’m hoping to avoid taking it to a dealer/repair shop at $125/hour for days of diagnosis. Thanks.