Tried Bounce sheets in a stored car. The mice used them to make nests!
The only thing I have found that they really don't like is used oil. I think the smell messes up their scent trails. Remember, it isn't the first mouse that causes the real mess, it is the dozen family memebrs that follow that scent trail. But of course, you can't use oil in your camper.
Maybe sticking moth balls in every potential external opening might be the next best thing. The trick is to keep them from getting in the camper, not trying to make them leave after they are already in. Good luck!