Dave-Sparky writes "I will have to disagree with the above statement regarding using the breakers. If you have turned off all the breakers, then there is no source for the current to be leaked from the neutral to ground."
OK, well say that you do have some minor leakage between neutral-ground on one of the circuits.
Having all the neutrals tied together WILL trip the GFCI.
How can this happen even after turning off the breakers you ask?
Simple, electricity will seek the path of least resistance and since all the neutrals are tied to the neutral buss you will affect EVERY branch circuit in the breaker box.
Removing all the Hot AND neutrals will allow to isolate each and every circuit until you find the offending one.
Doesn't matter if you turn off one or all breakers, it only will take ONE breaker turned on to trip and it doesn't have to be the circuit which the power is applied (remember all the neutrals are tied together).
mexbungalows writes "Hmm, would it not be easier to branch protect the circuit being used inside the RV? I seem to recall five decades of RV'ing without benefit of GFCI protection."
RVs do use individual branch protection, the problem stems from requirements for HOMES to have GFCI protection on ALL outlets which may have potential for being used near water.
The problem though when connecting a RV to a home branch which has GFCI you are now adding a large potential for false trips. Basically you are expanding the existing branch and adding a breaker box plus additional GFCIs.
Ideally (and this is what I did) you can have a 120V 30A RV outlet installed and plug your RV into that, no more false trips since the 120V 30A RV outlet is not required to have GFCI.
Are you saying that you think that the doubled GFI hookup is causing a false trip and I should just put in a designated RV outlet?
"First it would be helpful to understand why GFCI protection is important and what it does for a living."
GFCIs detect an imbalance of current between Hot and Neutral, basically monitors how much current is on the Hot and if the neutral current is not the same it will cut power to the Hot.
The idea is if YOU become part of the current return (IE you are a return path to ground and are being electrocuted) then you will reduce the amount of current on the neutral. When this happens then the GFCI will detect and cut power SAVING your life. The trip point used to be 10 ma but if I remember correctly that has bee reduced to 5-6ma and the GFCI must trip.
"Secondly, where GFCI protection would be moot or inappropriate."
Generally you can count on GFCIs on kitchen, bath, basement, outside and garage outlets.
In older homes it is not required to add GFCI unless you remodel (grandfathered) but I do feel they are something to consider since they CAN save your life.