Had a mouse in the Monterey storage bay the day I decided to clean it. We scared the crap out of each other and I never saw him again. It was the only Beaver mouse I ever saw.
Last year we had a mouse family move into the mini Tiffin. The only thing that works is the spring traps. Poison probably does too, but they might die and rot inside the rig somewhere. And, I don't like the idea of an eagle or hawk eating poisoned mice.
Once gone, there are lots internet stories about repellents. One is naked bars of Irish Spring. My mice ate Irish spring. The problem is how people say the repellants work AFTER the mice were trapped, dead and gone. Another is mint oil spread on everything. That stinks!
A weird issue with our Tiffin on a Benz Sprinter is the wires under the hood. Rumos suggest the insulation has "soy" in it. Weird as that sounds, apparently mice like to eat wire insulation.
For $50 you can buy a Rid-A-Rat. It is a small flashing strobe that (apparently) interrupts mouse sleep so they go elsewhere. I have that and three traps under the hood. I've not caught any in the traps since I got the Rid-a-Rat, so maybe it works.