We winter camp quite often. No water in any tank, down the drains, or shower. We use a port-a-potty so it can be dumped (wherever) and water is carried in with our 6 gallon water jugs (we have 4 of them). Water is caught is a tub in the kitchen sink, and just tossed out the door. We take cat-bath showers, warm water on the stove. We still like to winter camp with electricity, we are not boomdockers and we still go to State Parks that have electricity, but water, bathrooms, and shower houses are closed and turned off. So we use the port-a-potty and dump that into a pit toilet. (no chemicals).
Ours is mostly week-ends, so propane and electric usage is not an issue as we use both electric heat and propane in the winter.
Now, if the trailer was sitting permanent at one spot, I'd probably want to under skirt it and insulate it better too. But for our purposes, we travel around too much.
To successfully winter camp, you have to think of your camper as a glorified tent. If you were tent camping, you would not have running water and a toilet. How do you camp when using a tent? Tents don't come with stoves and televisions either. Do the same thing with your camper and you'll be successful winter camping in an RV... except you won't have to sleep on the ground! Absolutely no water in the camper's systems anywhere, and you'll be just fine.
