Okay, so in light of this discussion here's what I'm doing with my car. When I'm in town, and since my town is small ~30000, I think two or three wool blankets permenantly in my car is sufficient and probably the most practical. For out of town trips, either up to the mountains or highway trips, I will throw my newly acquired Army Modular Sleeping System into the car and my Thermarest pad. Under reasonable circumstances (even here in Wyoming), I think that should keep me warm through a cold night. The sleeping bags can stay unpacked and fluffy most of the time and only be compressed when I take them with me.

Question though. I have a Ford Explorer, so I can lay down the seats and sleep in the back. But will that be warmer then sleeping outside? I'll be out of the wind, but I've heard advice that you should shelter outside a car or aircraft since they can actually be colder (or effectively colder due to being surrounded by metal) then being outside as long as you're out of the wind. So sleep in the car, or set up camp next to the car?