I just finished a 9 day trip with the Dakar ADD-a-leaf in place, It made a huge difference
I even had an additional load of two boned out deer and the truck held its rake and felt tuned for the load, so I'm bagging the air bag idea altogether.
Another nice addition to the truck was a 12 volt bunk heater I found on ebay for $50. its 46" X 60" and just pins to the mattress under the sleeping bags and down comforter that I keep stowed in the tent.
It has a control switch that stays in the tent with settings 1-7 and supposedly has its own thermostat inside the controller to maintain the heat setting.
A 12-volt heating blanket is nothing like a 120 volt! it doesn't get hot, its actually hard to tell its working if you don't put something over it to capture the warmth. You can certainly tell its working after its been on a while and your laying on it.
It only got down into the 20's but the heating blanket kept the chill completely out of the tent, I didn't have to use the propane heater at all which is good because those create so much condensation that I've had it get completely wet underneath the mattress and ruin it with mold. Sneaky condensation doesn't appear on the roof where I could notice it, but it was certainly accumulating on the floor!
Now I can delete the propane heater (and bottles, since my lighting is electric and stove is unleaded) and make room for a 60 watt solar charge kit. The electric blanket does suck the juice (3.6 amps max) so it would need recharged every 2nd or 3rd night if its really cold and the truck isn't moving.