ditto the window thing. I spent a cold year in a camper in Colorado. It was well insulated, except the windows, which were really crappy.
I had storm windows made at a local glass place. They mounted on the inside of the camper windows with those little turny plastic thingys. They helped out a lot, but I can imagine what good windows would have been like.
And I'm a big fan of the electric heated matress pad. Not an electric blanket, mind you. Never liked those.