Good day all,
Slept in my car MANY times - Especially on hurricane chasing trips.
In the plains (tornado alley) chases, I try hard to find a cheap motel, but if it's not available (graduations in late May / Memorial day, etc) I pick a safe place (rest stop / truck stop) and sleep in car there.
Not comfortable, but you do have access to showers and meals at these places 24/7 (Flying J for example).
I make sure my seat can recline almost horizontally (SUV's great for this), or if in a van, a small inflatable bed is great. In a small car, reclining and a pillow light sheet to cover is good, and I usually leave the car running / air on if it's hot (but do this ONLY outside - not in a garage or such - to avoid carbon monoxide).
You can also use camping equipment and sleep OUTSIDE your vehicle as well, but that takes much space and all that. Also, a chase partner of mine told me that he had his tent "slashed" during a chase at a rest stop and stuff stolen from it.
I heard of tire slashing, but now "tent slashing"?
Makes me wonder.