I've actually had very good luck with the ultra-sonic pest repellers.

I keep one plugged in under the RV at all times (reminds me, I need to plug it in again after our trip last week).

Lowes & Home Depot sell one that has dual speakers. That's the one I use.

The only other suggestion is a boron based poison but then you run the risk of them taking a dirt nap inside your VX. Better off with the ultra-sonic repeller.

This is the one I use:

http://www.victorpest.com/store/mouse-control/m792