I tried ammonia soaked rags, placed in a couple of small, open containers while trying to dissuade the neighbourhood skunk from patrolling out side our bedroom window. Next morning they were all tipped over. Repeated, with the same result. Not sure if a mouse would feel differently ...
I did find a small nest on top the truck engine, that had been sitting in the driveway. Vacuumed it off and stuffed some crumpled up chicken wire in the space. Or maybe could use something like those bird spikes.
Also found 'sign' on top the Daily Driver engine at home. Know it wasn't there the day before. Both cases prob the critter was looking for warmth and a hideaway. All they need is a few hours.
I fully expect the overnight possibility when camping, esp in the bush. If you are camping in a previously used spot, I think the local small mammal population will be pretty tuned into quickly checking out your campsite and rig, at least where we've camped.
One morning, just after leaving camp, had a mouse pop out of the windshield wiper hole and scurry around the hood. No doubt he had had a rude wake up that morning ... and yes, they can hold onto a moving wiper blade very well, thank you !
And then there was the shy one hiding at the back of the trundle drawer. How he got inside there I'll never know.
We've found other stowaways but who knows how many have come and gone unnoticed. So far tho we've had no negative experiences, as long as we've kept the cab and camper closed up.
I know some folks who've had wires nibbled. They tried various deterrents without success before ending up trapping...