Since the economy turned down in 2007 there are numerous websites on this topic. Just go to google and search on homeless car living. There are so many issues for the nuevo homeless. Security, bathrooms, bathing, avoiding prosecution and persecution, storage, laundry, self defense, and on and on. They also spend a lot of time delving into scheduling because once you arrive at your sleeping location, you are pretty much stuck hiding in your car - so you have to take care of everything like bathroom runs and organizing prior to arriving at your sleep location because bathroom breaks and flashlight glow will give away your location.

There are also many campgrounds that will kick you out if you don't pitch a tent.

If you're not homeless, and you're only contemplating occasional sleeping in the car, then life is a bit simpler. One thing for sure is that you have to keep some windows cracked open to let out condensation. If you're in bug country, you'll need to rig up a window screen with magnets along the edge so you can cover an open window with screen material. Or, if magnets are not appropriate, then you'll need to invent some other way to cover a window crack with screen material somehow and still allow air movement.

It seems the number one issue I get from reading these sites is that prosecution and persecution are the two main scary issues for most people who are doing this. Cops and bandits become one and the same and avoiding both becomes a priority.