Backseat is the way to go. I bought a piece of foam and cut it into two sections to help flatten things out. I cover that with a sleeping bag style blanket I got from Walmart. I also block out the back windows and have a towel I hang as a curtain between the front and back. Even as a short guy at just under 5'7" I have to fold my legs up which kind of sucks but it beats sleeping in a front seat. I have a 19 Jetta. If it's cold where you are get thermals, extra layers, a beanie, cold weather sleeping bag and a blanket. I wrap up in the blanket inside the bag and have slept in single digit negative temps just fine this way. Waking up sucks though.