I never said Mike was wrong. GFCIs are permitted in older homes with no ground. And they work because of home plumbing being earth grounded by being buried underground. RVs do not have that same grounding and is a totally different story. That is why NEC specifies an RV using a generator must have a ground-fault path provided. Different requirement than that for an older home.
And I will ask you the same question. If there is no path back to the source power for current "leakage", how can an imbalance occur between the hot and neutral? That missing current can not simply disappear. And the same statement. Current can not flow without an electrical path back to its source.
I really want to know.