Here are some highways that have rest stops, sort of a mini park (mainly for truckers) so you can rest, park your car, and they usually have portable bathrooms, should be safe, warm up with your car's heater or just use lots of layers of covers. As for say a city or urban area, just park near a gas station or 24/7 fast food restaurant, maybe not on their parking lot, they might be assholes and call the cops. In a city always cover the front of your car (the 2 front seats) you should be sleeping in the back of the car, also cover the back so ppl think the car is empty. In a city, don't stay in 1 spot for like more than 3 days straight or ppl will notice a pattern, try recycling different locations. Make sure you know the parking times or you might get a ticket. Obviously avoid dangerous areas.