I think your issue is in the wiring also. The fact that you put a regular receptacle in there and the GFCI popped when you plugged into the house bathroom, IMO, negates a bad GFCI in the coach. Have you done any electrical work in the coach recently? Often, when replacing receptacles care is not taken to ensure each set of wires is installed in their proper place on the receptacle. Cross wiring will cause the receptacle to work but will trip any GFCI.....I would not use that circuit until I'd found this "issue"...Dennis