I always figured that if lightning has enough energy to travel 40, 000 ft or more through the air, it won't be stopped by a set of tires, or in this case, an inch of plastic. The reason you are generally safe in your car in a lightning storm is not because the tires insulate you from electricity, but the car acts like a shield... i.e. Faraday Cage.
At any rate if there is a voltage difference between earth ground and the chassis that is tripping the GFI, and if it is the result if mis-wiring, you could potentially get a shock when you step out of the coach onto the ground.
I don't mean to harp on this, but it could potentially be a safety issue. Enough that I would feel better if I got it checked out by an electrician... especially given the quality of work that we are accustomed to in the RV industry.
As I said though - potentially an issue - but not for certain.
The only thing that works on a RV is the owner...