Yup, heating mattress pads are great if you want to lay there and listen to the drone of the generator all night, or wake up to dead batteries...
You guys think that just running the pad a little bit before bed is going to solve this, but you don't understand that the heat transfer is happening any time there is a hot side and a cold side. The heat will be constantly sucked out of the bed, and will need to be replenished constantly to keep the bed comfortable.
That means the heating pad will need to run all night, which is not practical unless you have power. If I read my TC owner's club membership manual right, we are obligated to look down our noses disparagingly at anyone who would waste such a wonderful resource as a TC by staying in a c... c... c... campground.