I prefer a really hot blonde ... oops, sorry; what was I thinking? lol In all seriousness though, shared body heat under blankets, heat sheets, a sleeping bag (you did pack something, right?) is a great survival technique. Rover counts too.

Running the engine is OK if you've got gas to spare AND the exhaust pipe is clear. If you're caught in a snowstorm, there's the chance that the exhaust could be going into the vehicle. In terms of the whole good/bad thing, that would be bad.

Otherwise, maybe if you had a little camp stove, camp heater, or flame based lantern, AND you could crack a window, but carbon monoxide is always a major danger.

HJ