Try Bounce dryer sheets. They have prevented costly damage to my 
relatives high dollar BMW track cars that are garaged in a heavily 
wooded area for 30+ years. I have also recommended them with positive 
feedback to my own customers when working in several service 
departments. Position them under tires and in any area that you have 
seen evidence of infestation. Of course not near heat sources or moving 
parts. I quit using them in my dryer several years ago when my 
father-in-law passed from pancreatic cancer and used them in all of the 
laundry. Here's more on that lest a separate thread get started 
http://www.healingnaturallybybee.com/articles/toxin5.php. Sorry but I'm 
more concerned with protecting my vehicle and its hoses and wiring than 
contributing to a squirrel or mouses pancreatic cancer. Just what has 
always worked for me. YMMV.

David Clarkson
90 Westy outside in the woods with no rodent damage (but driven daily)