1998 southwind model 32v tripping GFI at campground power supply.there were 2 other campers having identical trouble whereas they had not experienced at other campground GFI shore power.After returning home i checked by plugging into my house 20 amp no fault circuit outside house and everything powers up normally.The campground electrican checked and replaced the power outlet and it was still tripping the GFI immediately when connecting.So i suspected trouble in the coach wiring.I have a continuity meter and checked the ground and neutral and is showing continuity at the 3 prong 30 amp plug . where would one start to look for a grounding if the neutral is the problem?