Some people want the underside of their cars to look as nice as the top. The main problem is bare metal such as drive shafts, and brake parts such as rotors will rust. This rust really shows when you have the open wheels as we have on our 2005. When do they rust most, in the spring and fall like right now when it is cool and damp. An unheated garage is equally cool and damp causing rust. If you are fortunate enough to have heat in your garage, it is a good idea to keep the heat on during the damp seasons to drive the moisture out. Once winter hits and things freeze up, rusting isn't a problem. I have the furnace on, spring and fall. It doesn't cost much and if I want to work on the car, things are already cozy. Right now, I am in the middle of changing the oil and greasing all our vehicles to be ready for winter so the heat is more than welcome. During the summer a good dehumidifier in the garage helps too. Just a thought.