FWIW, I thought I'd share an idea I put to use for winter storage: I found this at Home Depot for $29, an ultrasonic insect/rodent repeller. This particular model runs on a 9V battery (I'm finding that one battery last about 3-4 weeks in the outside cold air) or included AC adapterand I simply put it in the engine bay. I tested it on the in-law's cats, it at least repels them! I suppose one more in the interior would be a good idea if you believe in cracking the windows.

 

So how did it work on the in-laws?

 

LOL

 

The mice will just use this to keep the cats away.

 

I have one of these as well, The guy I bought it from insisted it would scare away spiders, as some of you know my biggest fear...Didn't work, so I tried it in the garage. I have noticed a big decrease in the wet foot prints up my car cover. Its not 100% for me, but better then nothing.