the best thing I have found is cats, and removing all food supplies for them. I store cars outside all the time and never have a mouse problem. Mice need two things to make a nest,
a food supply
and material to make the nest from. they rarely will travel very far from the nest to get food.
dog food in garage, bird food on bird feeders, and bags in car, trash cans trash bags ect will all generate those little suckers.
everyso often if you start the car and movethings around it discourages them.
moth balls are the best, i have herd they have non sented ones but whats the point of that its the smell they dont like.