Quick war story involving dealing with cold...
when I was stationed at Fort Polk, LA, I had a job that required me to live in the back of a Humvee for 2 weeks at a time. Canvas-top Humvees are not known for their insulation, and yes it can get relatively cold in Louisiana (20F high one December -- not cold compared to Alaska, but still unpleasant if outdoors.).
So, I took 4 extra feet of heater vent hose to the field once, hooked one end to the heater vent, stuck the other end in my rubberized sleeping bag cover.
Then, I made a huge loop of 550 cord running thru the interior of the Humvee, tied to the ignition switch.
If i woke up freezing cold, just reach out, give the rope a tug, wait for the orange glow-plug light to go out, then yank it hard till the engine catches. After about 20 minutes, the hot air heats up the sleeping bag, and I tug the rope the other way to cut it off.