The problem sounds like the hot wire and neutral are reversed. Start at the receptacle that powers the coach. If it is OK, then. Go to the shore power cable.
Then check the panel in the coach. The neutral should not be bonded to the ground.
You should also check to make sure the ground conductors are all tight and that there is a wire (bare # 6) going from the ground buss in the coach panel to the skin or frame. The attachment point on the skin/ frame should be clean and tight.
Also make sure the ground circuit goes all the way back to the house power panel.