“a 12 volt (electric) blanket”
Neat idea, makes my summary list (to be posted shortly).
The best thing you can do, IMO, is get yourself a good cold weather sleeping bag. Army modular systems can be found for less than $150 new. This way, you don't need heat at night even in zero degree weather as long as you are out of the elements.
I've purchased six of these for family members recently. :)