While your pride and joy is safely stored away for the winter, you need to protect it from another evil: mice. These creatures love to make a winter's nest in the safe confines of your stored vehicle. There are a lot of theories as to how to prevent mice from making a nest in your car. Some theories involve chemicals while others involve traps or predators.
Some people swear by dryer sheets. They put a few sheets inside the car and the sheets drive off the mice because the mice can't stand the smell. Others recommend moth balls (naphthalene) instead of dryer sheets. However, the moth ball odor takes a long time to dissipate and passengers in a a moth ball protected vehicle will smell of it even after a short ride. The US EPA has classified naphthalene as a Group C, possible human carcinogen so be careful about long-term exposure.
Mouse traps are great for trapping the hungry rodents. The clamshell traps are quite effective at trapping them and mice trapped in a clamshell are easier to dispose of compared with those trapped by a traditional mouse trap. The ones with an actuator-paddle surrounding the bait work better than ones with actuator-lever holding bait. Mice are often able to clean off the lever without being caught. Besides cheese, bacon and peanut butter also make good bait to attract mice. As with food, it will eventually spoil to the point where even mice won't be interested so periodic maintenance is necessary.
The best method of keeping mice out of your car is to keep a cat around it. Mouse traps work well to catch mice when they wander into it but there is no guarantee that they won't make a nest in your car first before they get caught. Cats, on the other hand, catch mice instinctively and seem to relish the chase more than the meal. As predators, they protect your car from mice proactively and you generally don't have to wait for the mouse to find the cat.
The main downside to having a cat is having to protect your car from the cat. Cats, by their nature, always love to perch in high places, which will invariably the hood or roof of your car. Even though they seemingly have soft, padded feet, they also have very sharp claws that aren't automatically retracted because they are walking across your fresh paint or even your all-original 70-year old paint. You can try to train your cat to stay off your car but you will probably have more luck telling the sun not to shine.
You can either keep yelling at the cat to get off the hood or you can find a better place for the cat to rest. The best method I have found so far to simply put a heated cat bed in a high and cat-accessible place but there is no guarantee that your cat will use it. You don't need much to make it accessible because cats are excellent climbers and jumpers. However, it almost seems as though cats will perch on your car simply because you don't want them to.
Besides their love of high perches, cats, by their nature, like to see what's going on in the world outside. If you don't have a perch beside the window, your cat will perch on the nearest best thing, which will likely be your car. If you make it soft and warm (old scraps of carpeting will do), your cat will have no reason to rest on your car (but cats aren't reasonable) when it has a much better place beside the window. These are easy to make but ready-made window perches are commercially available.
Another alternative would be to make a barrier wall around your vehicle with 24" aluminum flashing. Mice will have trouble climbing the slick surface and, although they're extremely good jumpers for their size, 2' is much too high for them. Set the flashing vertically on the floor around your vehicle and screw 2"x2" boards to the inside bottom of the flashing for stability.