Jack, I did a GOOGLE search on electric pest repellents and the list is quite large. Northern Tool.com lists 87 (I think) different types of pest repellents including a "commercial rodent repeller" for $29.00. I have used these repellers in my garage for several years, (mainly to eliminate spiders and such that we get here in Florida) they list mice and 20-30 other type pests that they control by ultrasonic frequency emmissions that humans can't hear. I had some evidence of field mice prior to putting the repellers in, haven't seen any sign since. I place several in the unused outlets around my shop because they seem to somewhat directional. If I need the outlet while I am out there I unplug it and put it back in when I leave.
All of that said, was based on your friend having electric in his storage area. if not, he may want to try mothballs, in containers around the outside of the car. He probably doesn't want to replace the smell of the rodents with the smell of his grandmother!
The phone number for Northern Tool is 1-800-221-0516
Gary #06984
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