This is what I've done when I've car camped on long trips lately.
Put up the big dome tent. Move all gear and bikes into tent. Blow up the mattress. Put it in the back of the Element. Sleep warm and dry no matter what. ;)
I even have reflective insulation for the inside of my windows, which I put up for privacy and insulation. I can turn on the radio in the car when I want to hear the weather.
Karen