I had a friend who did it for 2 years, he rented a storage unit that was big enough for his car after a few sketchy nights. Put the car in and pull the door down, set up the cot, unroll the sleeping bag and settle in for the night. It had the added advantage of not having to keep all his stuff in the car at all times so he could maintain some semblance of a normal appearing life.

We had no idea he was doing it.