Have mentioned this before but, having heard that farmers deter mice from attacking stored machinery using moth balls, I have done the same. I place four moth balls in a small nylon mesh bag - hang one on the front chest of drawers, one on the oven handle, one in rear of van plus one more wherever convenient. Makes the 'van smell like Grannies wardrobe ( think Giles cartoon type Grannie ) but the smell soon goes. Moth balls 'dissolve' after about four months so need replacing - depends on the temperature. Main problem is finding them in shops nowadays so if you do go down this route buy a couple of boxes when you can. Now whether moth balls are effective I do not know - I have not been visited by mice though and the 'van is stored on a farm.