Weekend camping is one thing..a long winter trip or camp is quite another. Big Foot and Trple E's, as mentioned are both really good three season units. Thermo windows, heated tanks and well insulated and the lines are insulated or embedded in the body.. The heated tanks thing is a bit of a mis-nomer. They are heated using ducting thru the furnace system. You could add heat pads to the tanks but then you have to have power to make it work. So..if you aren't cranking the furnace..you tanks are subject to freezing. One can counter that with a dose of RV anti-freeze or a cup of course salt. If you are camped with power..you aren't likely using the furnace, so much as a heater, right?
The on board fresh water is more likely to be ice free because it is inside. You can open up the settee and let it stay at room temps.
Weekends are easy...much longer and you want to ask around and get some insight on how folks handle it.
Gary Haupt