Tripping gfi in garage when plugging into garage

Trip all circuits in motorhome to off. Plug in motorhome to garage gfi. Turn on and then back off each motorhome circuit until gfi trips. You now know what circuit in the motorhome may have a ground fault or has a appliance on with a greater than 15 amp draw such as the AC, Water Heater, microwave, etc. If none of the circuits trip the GFI by themselves then turn on one and then the next until you overload the gfi. At least you may be able to isolate the cause somewhat this way.