I have, on occasion, rested a few hours in a church parking lot, well away for the buildings.
If there is a truck stop around I get fueled up and park with the big rigs, but try to stay out of every ones way.
If I were really at wits end, I would ask the local police station if I could park in their lot and explain that I didn't feel safe driving when I needed sleep. (Ask if the have a coffee fund and donate 5-10 bucks.)
I would be a bit uncomfortable just parking anywhere due to not knowing the neighborhoods.
I agree with the person about Campgrounds-----------Just for sleeping there is no way I'll spring for the price to park for 6-8 hours. We aren't poor but we aren't in the Bill Gates set either. I just like to be frugal in my retirement years.