Winter use..... I travel to warmer climates in the winter and have gotten caught in cold weather. I found the furnace
can keep up at pretty low temps. (we were at 5°F) But, it did go through a lot of propane
and no pipes frozen.
Let me give you my configuration as far a water. 12 Gallon fresh water tank and a 26 gallon gray water tank. All the fresh water, tank, tubing(piping) are inside the shell. The gray water is underneath floor in the dinette area.
I never let the inside get near freezing temperatures, 45°F is about as low it ever gets (I run the furnace
all night with approx. 50°F thermostat setting.
A bit of thermodynamics information might help. With all the fresh water inside the shell and the fresh water tank kept over 50% full it's going to be pretty difficult to freeze. The gray water tank will have soap, coffee and other stuff in it which lowers the freezing point. Also since it's protected from the sky it's less likely to freeze.
I hope this helps with your decision.