I know your frustration! I live on an acreage here in sunny BC and found that mice preferred my 300E over my pickup, van, and anything else that was parked here. At least they had some class! They would nest between the valve cover and the hood pad. They would also make the nest literally overnight and I learned to check the car every morning. Fortunately, there was no damage other than the mess. I was able to control the mice by continuously setting hair-trigger traps baited with peanut butter. I put one on the valve cover and another on the bumper strut just behind the radiator. I won't use poison because of the downstream issues of poisoning other critters. Caught about 4 before I finally moved the car to a garage. No problem since. Thankfully!

On another note, within a week of buying my Mercedes I had a bear scratch the paint. There was a mom and two cubs that liked the car (did they smell the leather?). I couldn't tolerate that so the dog went outside and that ended the bears roaming around the house.

Best of luck!