Please don't. 12V inverters that are more than about 300W in capacity are: 1. Really hard on most vehicle charging systems 2. Require way bigger cables than most people use, thus creating a fire hazard 3. Are super inefficient as a system, as nearly any sized gas generator is significantly more efficient than a setup like that 4. Idling a vehicle with a significant electrical load at lower RPMs is horrifically awful for your alternator and possibly even cooling system, even in a very cold environment Sure, do what you gotta do... But you gotta at least do it right so you don't roast something and make your situation worse.