We found signs of mice when we got our Eagle TT out of storage. I had taken measures to keep the little buggers out, but apparently that didn't work. I believe that eliminating ways of getting in is more effective than trying to repel them after they're already in.
I found some holes in the floor where wiring and plumbing pass through the floor, namely behind the power center (CB/fuse panel) and under the bathtub at the drain P-trap.
I got some Great Stuff spray foam for pest control and shot it around as many spots as I could get access to. I think I got all of them except under the bath tub. That's a bigger area. I'm thinking about a sheetmetal plate to block the area off.
I was able to do that with my last camper and never had a mouse get in. With the thermal package on my current TT, that corrugated plastic has to many seams with the slide outs and it makes it difficult. I might even remove it.