Keeping mice out

Anyone have proven ways to keep mice out of a car during storage? I've tried spreading mothballs all around the area and putting Bounce dryer sheets inside the car to no avail. My 97 Bird only comes out a few times a year so they have plenty of time to find their way into the trunk and engine compartment.

Get a cat

get a motion activated turret set up at each corner of your car, line up 5 rows of mouse traps along the whole perimeter, sprinkle rat poison everywhere imagineable, build a standing moat full of battery acid, and put a python in your trunk. Worked for me. Roaches however, are a different story.