Have seen this problem far to many times. Something is connected wrong.
I will repost a previous reply. Yoru really need to purchase one of the checkers that is In The post. Then, use the checker to test the shore power B 4 you connect the camper then immediately check all receptacles in the camper to insure it all tests OK. The 3 lights
on the checker will point out the problem.
Should you still have the same problem after the checker states it is OK, then get an electrician to check things out.
AC Wiring: White to lite and green is ground the world around.
What this means is that the white wire is the return and attaches to the shinny silver colored screw and the Black is the HOT wire and attaches to the brass connection and the Green is ground and attaches to the green connection.
On my camper, the white is also attached to a bus that has a wire attached to the frame of the camper.
You will need one of these to test to make sure all is correct.
Electrical Receptacle Tester with GFCI Diagnosis
Use that device each and every time you connect to a power source. Check the power source B 4 you connect then once connected, go inside the camper and check to make sure it is OK.