I've camped for up to a week at a time with night time temperatures in the mid 20's in my Miramar. . How I do it is I go ahead and winterize the lines and empty the fresh water tank.
I use gallon jugs of water and a couple gallons of RV Antifreeze. I wash up like my parents used to do it... They called it a sponge bath. Never used the shower. Washing up with cold water is invigorating!
I used the antifreeze as a chaser to make sure my black/gray water valves wouldn't freeze. As long as the temperature was above freezing when I dumped I never had a problem.
You will go through a lot of LP at that temperature so I supplement with a space heater. During daylight hours the furnace barely ran.
I found the lack of worry about lines freezing made for a great time camping.
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