I work at Ford Heavy Truck dealership and we see rat damage all the time.... Not cheap on the average.
At a dealer/auto trade show I saw this electronic box that you mount in your car. Low draw on the system, and emits a sound that rodents don't like. I wish I still had the flyer for the company, but I tossed it a while ago. Although there is products like this all over Amazon with decent reviews. Might give that a try
