When we travel in the Winter we keep our fresh water tank topped off close to full at all times. We only hook up the hose to shore water to top off our tanks. If it is expected to stay at 25 or below, we put a 100 Watt incandescent bulb in the wet compartment using a thermostatically controlled outlet and a mechanic's trouble light shield. This keeps our pump and water lines from freezing.
For heat we never use the furnace unless we want a quick blast of heat for some reason. We use an electric blanket, electric space heaters, as well as our roof top heat pumps. If it is going to get below about 32 degrees, we use a portable internal heat pump that is not affected by outside temperatures. This has kept us warm to single digit temps below zero. We keep a dash fan blowing to keep the windshield clear since we use a curtain to close off the cockpit instead of the pull around drape.
We prefer to travel in the Winter and have camped in the Grand Canyon in January and many other places where the snow can get deep. Our dog loves the snow and we love not having to fight the crowds, which is one of the reasons we leave Florida during the cooler months.