Mice: What man doesn't love a woman screaming at the sight of a mouse????
Best deterrent is to keep all food covered and make sure there are no tiny holes in the camper that allow mice to squeeze through. To check, wait for dark, light up underneath the camper (or basement area), go inside the dark camper and open cabinet doors and look for slivers of light. Fill with steel wool and expanding sealant.
Ultrasonic pest controllers do a pretty good job. In some cases, putting dryer sheets into all the recesses of the camper can deter mice and leave the camper smelling nice. Moth balls in a plastic bag with holes poked through work great, but I can't find a single way to get rid of that stinky moth ball smell except time - lots of time.