We used an old water bed heater on the Class C in TN/NC mountains (we junked the king water mattress when we moved into the CLass C.... the king size 4 poster frame was cut down to fit a standard full size mattress and is currently in the bus). In NM (similar temps) we simply built a foam board box (1") and stuck a 40 watt incandescent light bulb in there on an extension cord. The cord plugged into an Easy heat thermostatically controlled plug that we then plugged into the power post. We have also used Frost King pipe heat cable quite successfully. Depending on where you are wintering at (we get below freezing) a couple inches of foam house sheathing with little heat applied goes a long way to preventing your tanks from freezing up. I have found that our drain valves will freeze up long before the tank. That's why we wrap pipe heater cable around the valve area. We have had a tank freeze. It was not fun. Luckily it warmed up for the next few days and we finally got it thawed... and then we boxed it in. We had been told repeatedly that "it doesn't get all that cold here".
BTW, we replaced a standard RV black tank valve while in South Ga from an overnight freeze.
Since we will be spending at least two more winters in a place that does freeze and snow (freezes more than snows) we will be insulating our tanks and running a duct from our house heater. We will also include a duplex electric outlet in the bays. We use a home made insulated/heated water hose (requires electric) and want to be able to stick a light bulb in there as well. I want the heated water hose to be plugged into our bus. If we lose power, it can be powered off the generator. We have lost power in the campgrounds for about an hour once or twice. But I well remember losing power when we lived in a house for days during the winter (used have an annual Thanksgiving Day and Christmas Eve power outage). A couple winters ago, my mom lost power for a week during the winter. Which was better than my cousins who lived farther from town... they lost power for a month.
For the bed, we use a heated mattress pad, the kind you sleep on top of not under. We think it works better than a traditional electric blanket and the model I have uses 70 Watts max 110-120vAC (that's what it says on the back of the controller I just looked at). I "store" it on the bed.
We put a 0°F sleeping bag (opened up) on top of the bed as a comforter. We have been sleeping on a cheapie Ozark Trail (Wal-Mart) air mattress with a 3" or 4" memory foam mattress topper. The heater pad is on top of the memory foam. We used the mattress heater a couple of weeks ago when night temps got down to freezing. Beats turning on the space heater.