If you are getting shocked when touching the metal on the trailer the chances are that the hot leg and the neutral are reversed. Or you have a hot wire touching the metal part of your trailer. In either case you have a problem with the earth ground connection as well.
You should have an experienced electrician trouble shoot the problem. Also tell him that the neutral should not be grounded to the trailer frame. Only the earth ground and DC common should be connected to the frame or skin of the trailer.
If you have the experience and knowledge you can trouble shoot it yourself.
But you need to get the problem fixed soon.
Knowledge: "A gift to be shared. A treasure to receive."