In your electrical system (120volt side) The grounding conductor and the neutral conductor (white wire) should not be joined together or touching. Had a similar problem, plugged into campground power and it would trip the 30 amp GF breaker. Found some faulty wiring at an outlet, the bare ground was routed close to a white wire which had improper stripping and the two were barely touching. Yes, its a witch hunt but that is where I would start. Use a volt-ohm meter to tell if they are joined somewhere. Go to your RV plug and test the ground and the white. If the needle swings (analog) it is shorted together. Good Luck.