gfci still tripping

[Robin]

Well, I've completely removed both my PowerWatch reverse polarity indicators to
re-do them. Decided to check the coach with them removed and the GFCI still
trips when I plug the 30 amp cord in. It trips when I plug it into either of
the two 30 amp receptacles on the coach. (I do not own a 50 amp cord.) Trips
even though all the breakers are off including individual circuits, main breaker
and the separate 30 amp disconnect breakers. If I switch the master shore power
switch to off, gen or 50 amp it does not trip. It does trip if this switch is
set at 30 amps. If I start with everything at off, then gradually flip switches
it seems to barely hold, but if the switches are on and I plug in the cord, the
GFCI trips, suggesting I am right at the trip point.

One possible problem area is the genset which has been replaced in the past, but
does not ever seem to have been run prior to my getting the coach.

I am looking for advice on the proper troubleshooting technique for this
problem.

John Churchill
1980 FC33
LARGE MARGE
Sanibel, FL