[RussWhite]

Steve,

Hi - Everything Tom says is correct of course. What I have found that might assist a little is to help the person with the problem understand how a GFCI operates. Once this is understood one can decided if he wants to chase for the problem like chasing for an air leak :-)

A GFCI has a coil around the hot and neutral conductor. This little coil has the property that its output is zero when all the current that flow out through the hot returns through the neutral. It is happy and does not trip. The amount of current doesn't matter as long as it is less than the rating of the breaker. BUT, if some of that current ( an itsy bitty bit - just 5ma ) finds some other way to return - GFCI trips in the blink of an eye.

So - if the neutral is connected in any way to ground you have a problem. I often troubleshoot this with the ( usually boat in my case ) disconnected from shore power and use an ohmmeter between ground and neutral. You have to disconnect neutrals until you get essentially infinite resistance between the neutral and ground at the input to the coach/boat. This can be very time consuming - but I have not failed yet to finally find togetherness hiding somewhere. The older the coach, the more likely the insulation between neutral and ground has deteriorated. Sometimes you might get lucky and it will just be a wiring error in the main distribution box. Someone got the ground and neutral reversed at some point.

Normally your coach only has GFCI protection on a few circuits judged to be candidates for human contact between hot and ground. So I don't see a real hazard in operating the coach from a not GFCI protected 20A circuit. It's just that it can be hard to find such a circuit when you need it.
Hope this helps. Russ

Edit - this just popped into my mind. There may be a circuit on some coaches that causes problems with the GFCI. I am remembering some posts from long ago. IIRC the circuit involved a warning lamp that was supposed to warm of a reversed neutral connection. That circuit somehow may have connected the ground and neutral together in its operation. I am really reaching here, but I believe it was connected on the input side of the main breakers - such that it was active even when the main distribution breaker of the coach was turned off. I think on those coaches there were volt meters or lights that worked even when the coach main breaker was off - just needed power from the post to activate them. Just something to consider...