When we camp in the winter, we just use the heated washhouse. Our toilet is just a night time pee pot so we do not have to trudge over to the washhouse in the cold and dark. We flush it with a pitcher of water.
We carry a seven gallon jug for water which is enough for a weekend of cooking and coffee. We heat water on the stove and only use the bathroom and kitchen sink sparingly
We can keep the TT in the fifties during a sunny day with just the electric heater. Usually we are out hiking or snowshoeing during the day.
The real issue is when we are back home. Since we have not used the water so it still has the anti-freeze. But we have added a few gallons to the gray tank and a bit to the black tank. So once we are home, I pour about a half gallon of anti-freeze in the bath and kitchen sinks to re-fill the "P" traps under the sinks. Then, maybe a half gallon down the toilet into the black tanks.
However, if we take a true winter break for a few weeks down south, we just have to re-anti-freeze water system.
There is nothing difficult about that, I open the low point valves and let the water drain out and reclose them. Then I use the water pump with the input connected to a hose stuck into the antifreeze jug and pump water through the facets until they run pink.
With our TT a sustained temp in the mid twenties will freeze up the pipes over night if we do not run the furnace. So we prefer to dry camp and use the electric space heater.
Twenty six foot 2010 Dutchmen Lite pulled with a 2011 EcoBoost F-150 4x4.
Just right for Grandpa, Grandma and the dog.