I've tried lots of stuff, but the best solution (for me) so far has been Grampa Gus peppermint pouches and bleach. For some reason those little buggers love my dually. Winter or summer they get in it...I don't drive it in the winter and at least weekly in the summer but constantly see signs they have been there. I leave snap traps, Bait and Grampa Gus pouches in there but if I do not routinely pour bleach around the perimeter of where it is parked they come back. I also bleach around my enclosed trailers. I got this idea from watching a Documentary on rodents. I learned they are "Scent Hunters" meaning they search for food and shelter following scent trails left by themselves or other rodents. Bleaching the perimeter breaks the trail. Another similar option but not easily done its to disturb the ground cover (aprox 24") around a given habitat area.