To the OP:
There are several causes for your situation. Since your outlet has not worked for some time, you should inspect them one at a time, starting with the easiest. Here's what I would do.
Make sure ALL electricity is [COLOR=]disconnected from the coach, including generator and auto start feature, if you have one. You want ZERO surprises!
Go to your nearest Home Depot and pick up a new GFCI outlet. They will allow returns if yours is still good. Replace the outlet and see if that corrects your issue.
If that does not fix the problem, you'll have to check out the breaker. GFCI breakers MUST be installed in a certain way. To prevent constant tripping, you MUST connect LOAD Neutral to the circuit breaker neutral terminal, NOT panelboard neutral. Ensure yours is connected correctly.
Hope this helps and please let us know what you've found....Dennis