So maybe the best choices mentioned so far are really the various plug-in 12-volt heaters, or the dogs. (Yes, the alcohol also has its serious problems ...)
I'll stick with the dogs for several reasons....No power drain on my battery, No extra expense (I already have to feed em) and I will have them along anyway....

Oh, by the way: In case you are wondering, I am not a medical doctor.
Darn.....I was all set to tell my wife I had medical advice that it was beneficial to sleep with my dogs.....of course she doesn't really care since she sends me to the dog house quite often
actually we had already considered one of the 12v blankets. She gets pretty cold and when she's with me that seems the best way to go....she claims the dogs smell and she definantly won't go for the alcohol idea....fussy woman.....
Les