Do it all the time when travelling. Coldest night -23F in the Adirondacks with an ice climbing buddy. If I had a dollar for every night spent in the back of one of my Subaru wagons my bank account would be bulging, frome East coast to West, in any weather in any nieghborhood (sometimes scary) Now it is mostly while on business trip delivering loads with my Ford crew cab dually, VERY roomy (the kids and I call it "La Hotel,Da Ford"). Walmart are good bets as they ALLOW overnught sleeping in their lots, FYI. Most are 24 hour and you can use the "can" and stock up on forgotten items. My 9 year old has spent as many as 100 days a year in my truck in the driveway, coldest to 16F with my mountaineering bag. We had to tell his school that, Yes, he is sleeping in my truck and that it is safe/warm and of his choosing.

Ironwood