Mike, Last year was the first year owning a 5th wheel and soon after parking it for the winter I noticed we had a mouse.
We had the camper plugged in (to 120v) all the time so I bought some Black and Decker plug in rodent repellers (don't know the proper name of these things). The type that give off some annoying frequency that rodents dislike. It worked, after that I never found any sign of mouse activity.
I don't know if this will work for you in your situation, but they do seem to work.