I had a GFCI episode inside the RV that turned out to be the white wire going into the back of the GFCI receptacle having a cut in its covering, farther back before getting to the receptacle, so some copper was showing. This copper was touching the metal box the receptacle was in, and that metal box was of course "grounded" with the usual bare copper wire for that.
Once I found that cut and got it all proper, no more GFCI popping from that cause. The receptacle was ok, it was that white wire touching a grounded metal part behind it.
If that metal box were not "grounded", would the GFCI still pop?
OR --if there is no ground, how can you have a "ground fault"?