Never had problems with squirrels and my vehicles... The mice got in there first. The squirrels developed a taste for my cabin siding - T-111. I guess they liked the glue or something. But they chewed it viciously... Particularly on the front porch. I tried all sorts of repellants, including the hot pepper stuff. I think they just liked the extra flavor, because it didn't help. I shot some, and asked local squirrel hunters to shoot some, and finally replaced part of the T-111 wood with a simulated T-111 concrete board. They don't like that. My family dogs and cat keep them away from my home, but the cabin is still vulnerable. We shoot about 20 or 30 in that area each year, but they keep coming back. Game folks advise me that experiments have shown you can wipe out 75 percent of the population one year and they'll be back in full strength in the next year. They are indeed rodents.
I guess the problem is that men drastically reduced the population of foxes and bobcats around here, so they just don't have enough predators. The coyotes are here now and helping a bit, but they aren't a cagy as the foxes and don't get as many.