GFCI still trips

[Robin]

Well, I've completely removed both my PowerWatch reverse polarity indicators to
re-do them. Parts are on order. Wires are all disconnected and capped.
Decided to check the coach with them removed and the GFCI still trips when I
plug the 30 amp cord in. (I do not own a 50.) 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