Several years ago, pre-campervan, I would camp with my GF. We would take her Toyota Sienna Mini-van to the desert, the racetrack, etc. Not the best camping rig I've owned, no the worst, either. It came with a V6 and factory tow package, I added a brake controller and class III hitch, rear air bags inside the coil springs, it was a decent light duty rig. On this trip, we were flat towing my Suzuki Samurai Tin-Top behind on a towbar.
After a 6 days of December exploring Mojave National Monument, Death Valley National Park, jeep trails by day in the Sami, sleeping inside the Sienna on an airbed, cooking outside, it was time to head back to reality. Temps were a very comfortable dry 70's during the day, 40's at night in the desert. A great trip!
Heading home to the SF Bay Area, we took the scenic route, out through the west side of DV, through Lone Pine and hwy 395 north. I got tired, real tired around Monmouth Lake ski area about 11pm, pulled off to find a semi-secluded place for the night.
I checked the weather app on my phone, 19 deg predicted for the area over night. Our sleeping bags were not all that great, rated down to 35 I think, but I've slept in my bag in colder temps, on a thermorest pad on the ground in a tent. Surely the 12" thick air bed inside the van would be much more comfortable.
About 3am, I got so cold, I couldn't get back to sleep. I added more blankets to the top of our bags, started up the van and ran the heater for 10min, but our bed was just so darn cold, all I could do was cat nap for 10minute intervals, and wake up shivering. My GF was having the same problem.
After tossing and turning 'til 5:30am, her too, we decided to dress, turn on the heated seats and hit the road in search a 2 HUGE cups of coffee, breakfast, and maybe a wood stove to back up against.
During the 8hr drive back home, my brain was chewing on this puzzle "why was our bed so dam cold?" I've backpacked, goose hunted on frozen fields, camped a fair amount in winter, even storms. I couldn't figure out what I had missed.
Then it hit me, an 'ah-ha moment', upside my thick head like a frozen cod.
It was that airbed. Then air inside the airbed we were sleeping on, slowly dropped to some equalizing temperature with the air inside the van, maybe 20deg. Unlike a thermorest pad or 2" camp air mattress, our bodies don't put out enough heat to warm such a huge volume as a 12" thick, queen size, blow up air bed. The mattress side of our sleeping bags offered little insulation, since our bodies push out most of the air, and mat down the fiber fill. Lesson learned.
A few months later, I owned a 4x4 camper