In 2015, I spent about 6 months on the road while delivering RV's from the manufacturer to the dealer. I came home every weekend, but I "camped" in my Sonic during the week. By the way, the Sonics with the 1.8L can be towed 4 wheels down while in neutral. 1.4L autos can't. I towed the Sonic behind the RV, made the delivery to the dealer, and drove my Sonic back to the pickup lot.
I couldn't use the Air or Heat (not the dash stuff) in the RV, and it was usually too hot or too cold in the RV for sleeping, so I got very good at sleeping in the car. I am a big guy, but I was very comfortable in the driver's seat. I require a CPAP machine, so I used a 400W inverter plugged in to the cigarette lighter.
I typically ran the car overnight so I could make it pretty cool, and pull a heavy comforter over my head to block light/streetlights/noise (usually in Walmart lots). It would use 1.5-2 gallons over 6-8 hours. Much cheaper than a motel or even running the dash AC/heat in the RV (usually the Ford V10 or Chevy 6.0).
With my Igloo Thermoelectric Cooler next to me, my XM Radio for Braves games, control of the thermostat, I was as happy as a clam.
I wrote all that to say this: The 400 watt inverter was helpful for various uses. Might consider one of those.
Larry