My first question is what temp are you keeping the rig at night? Do you heat it solely with the furnace? If you say you are reluctant to use an electric mattress pad, or blanket is it because of the "cautionary" tales on here only? Im going to suggest that there are a LOT of rv.net users that rely on ceramic heaters, electric mattress pads and blankets on an ongoing basis. I would get her a quality electric mattress pad with a shut-off and give it a try. How about the hot pads filled with wheat that you heat up in a microwave and then place next to you as you sleep. Hot water bottle maybe! Lots of ways to keep folks comfortable.