Reddit mentions: The best deflectors & shields

I'm a semi retired guy that delivers RVs to pass time, often in the winter getting ready for the summer sales season. I do this with a crew cab pickup. In general staying in hotels makes the whole thing financially unfeasible, so most of the time I sleep in the back seat of the truck at truck stops or rest areas. I've done this in 20 below temperatures and though I won't say it's cozy and comfortable, it is possible.

Outside of idling the vehicle all night like a semi, you need to crack a window. You can suffocate if you don't. I highly recommend getting a set of these to keep out rain and snow. Crack it just enough to see light.

There's no getting around this is going to get cold. You need a subzero type sleeping bag. Blankets won't do it. Get a full bag. This makes it survivable and miserable, but you are going to want auxiliary heating. A 12 volt heater does the job. It's not going to make it room temperature but it will keep you from freezing. Unless your 12 volt system can be disconnected from the vehicle battery you are going to run out the cranking amps. This would be bad. So get one of these with a 12 volt cigarette lighter type plug and it will be enough to run for a couple of hours. I recharge mine through an inverter while driving. This also gives you a USB plug to run a phone which can be nice.

You have choose a life style that there isn't any great solution for, but myself and my fellow delivery drivers find this system works. If there's a better way I'm not aware of it. If you can't be happy with things this way, you choose the wrong way of life.