Bounce dryer sheets and moth balls will not deter mice! I had mice on two different occasions in my Sunline, and I was using moth balls and dryers sheets while stored. As it turned out, it was my fault as I left an opening for the mice to get in after replacing the hose for the fresh water tank.
The only gurantee against rodents is to maker sure there are no openings that they can get through.
And now, I'm just as glad that I'm not using mothballs! We still use dryer sheets to keep things smelling nice.
As for moisture, never needed anything for western NY winters...just kept the roof vents open very slightly....but my trailer was always stored indoors for the winter.