Just a question. Would using one of those little 3 prong to 2 prong adaptors have worked since it cuts out the ground?
Sometimes. Yes. But. ........
If the ground fault is a connection between the ground and neutral (green/white) on the coach then the 3 to 2 adapter will let you hook up. Whatever you have for a ground fault still exists - you've just masked its effect.
If the ground fault is an alternative path to ground - ie. not through the green wire - then the 3 to 2 adapter won't change anything.
I can think of situations where the 3:2 adapter might be an acceptable risk -- FOR ME
--- but I can also remember homes that were wired with only 2 conductors. We don't do that anymore either.
Ultimately this comes in the category of "if you have to ask the question then you shouldn't try it at home".