The problem with your rest area theory is that even though you haven't been a victim of crime at a rest area, there is a documented record of it happening. People have been killed or seriously injured as victims of crime doing exactly the sort of thing that you are promoting. Just because you haven't been a victim (yet?) doesn't mean a problem doesn't exist.
Ironically, your premise that sleeping at a rest area is ok because you haven't been hassled by cops is exactly one of the reasons why they are not a safe spot to sleep. Rest Areas don't usually see a lot of patrol car traffic and they usually are in relatively remote locations which is why they can be a prime spot for a criminal to take advantage of an opportunity.
Again, no one is saying that sleeping in a car isn't possible or that it won't save money, but there are ways to do it that are much safer than stoping at a highway rest stop.This is another idea that I simply would not recommend. There is a reason Coleman puts for outdoor use only warning labels on camping stoves. A car seat just isn't the most stable place to put a burner element, thus creating a significant fire danger. There is also the real danger of Carbon Monoxide and other gases created by burning propane in a small, confined space like a car.About cooking on a coleman stove. This can be done out of your car. You use the car doors as wind breaks and sit in your seat as you cook.