Electrical Prolem

I have a Big Country 3250 and when it rains the BFI outlet kicks out and also when I washed the trailer the other day it kicked out when the slides were in and I hosed down the left side.
Does anybody have any suggestions?

The GFI has a specific purpose. That is to trip when it detects moisture. So I guess that yours is working.
I would check to see that the outside recepticle cover has a rubber gasket and is sealing properly. Also I would check for caulk around the cover plate.

Peace
Dave