I use my TT all winter long. As for the water system I drain all the lines in the fall, RV push anti-freeze through the lines until I am happy with the level of protection. When I use the TT I have a small separate water heater( not sure the brand all the outdoors stores have them ) that uses 16oz propane bottles. I heat water in a 5 gal can, then set the 5 gal can on the bathroom counter. Stand in the tub and use the hose from the heater and take a shower. Just pour a 1/2 gal of antifreeze in the drain you used.
Do not wet up your whole system, just the shower drain. I leave my grey tank open and dump on the ground. I only use the tub, do not have to mess with anything but the one tub drain.
Been doing this for 10 years and no problems. After a long day of hunting, skiing or whatever a good, hot shower is almost as good as a cold beer.
Forgot to mention I am in North Dakota and have stayed in the camper at -22 below zero and have no problems.