the WORST kind of mouse infestation occurrs when the buggers enter your exhaust pipe and set up housekeeping in the engine. In cold weather, what attracts them is the engine heat from the 'pipe. Many engines on older cars ruined by mouse pee, etc. Solution has been to cut a slit in a tennis ball and fix it over the tailpipe opening.

To keep mice from the interior, moth balls seem to work...also placing some of the "mouse motel" traps underneath the car.

This is a big problem with many people who collect and store older cars.