I have "camped" in my Explorer before. Laid down the 60% seat, inflated an air matress, & rolled out the sleeping bag. You can crack a window to help with condensation. I found it quite comfortable. I personally did not find it particularly any warmer or cooler than sleeping in a tent under the same conditions. If you leave the vehicle bottled up, the condensation would make things damp, making the air chillier. A tent in similar weather, depending on the tent, you might have more "fixed" ventilation than what you want in cold weather. Cracking open a window would give "controlled" ventilation in a windproof container.