I agree with Bob. If you are planning only a couple days at a time in the extreme cold, I would carry the water inside the coach. You will find at that cold of temperature, you may have frost on your windows and/or window frames. Any snow you track into the coach will like freeze on the steps. The walls will be very cold. You will need extra space heaters inside the coach. I doubt you can keep the fresh water tank and unheated lines from freezing. It doesn't take long at 20 below.
I have camped at 15 to 20 degrees above zero for several days without issue but even then, I haul my fresh water inside the coach. There is just too much risk of damage in areas you may not even think of.
If you go forward, keep us posted as to how it goes.
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