The best mouse preventative is to seal up where they get in. The standard technique is to get a large light, crawl all over the unit into every crevice on the floor, and have someone underneath spot where light is coming through. Then, spray foam insulation to fill these areas. Additionally, crawl under the vehicle and look for the holes/cracks yourself without someone being in the unit shining a light.
For every person who says dryer sheets work, another one tells you about how the dryer sheets were chewed and provided excellent nesting materials for the mice.
Every article I've read says the best way to deal with mice are the traps. All the various products and 'common-wisdom' techniques are largely ineffective.