I used mothballs for years as part of the winterization process pop-ups and in our Sunline TT. I found out the hard way that it doesn't repel mice. So...I see no reason to use them again considering the health risks.
Likewise, dryer sheets do not repel little critters...had them in the very cabinet that the mice invaded!
The only way to prevent mice, aside from traps and rodent poisons, is to make sure that there are no openings for the mice to get through. My problems were my own fault. I had to replace a water inlet hose, and forgot to go back and seal the opening that I had to make to replace the hose. Once the hole was sealed...no more mice!!