MICE!!!

IMHO the real cure is to seal all the holes with spray foam. For larger holes you might want to use steel wool too. Get under your RV and look for any sign of a hole, and seal it. I did that and I still had the occasional mouse. I had forgotten about the place the power cord comes into the RV. I sealed that with a metal plate cut to fit and attached it with duct tape. No mice since then.

How do I know? I have no problem killing mice. I keep a trap and haven't caught a mouse since I sealed the power cord entrance.