I have an older Bigfoot (2000), 27 foot.
It is 4 season, built in Canada where it is cold.
It has a big 35,000 BTU furnace that 2/3 of the heat goes to the enclosed tanks. Those enclosed tanks include the pull valves being enclosed.
Dual pane windows.
The water tank is under the bed on top of the insulated floor.
The water lines are run through the heater ducts.
Two 30 pound propane tanks with room to add 2 more 30 pounders in the compartment if you really want to stay in sub zero for a few days.
As long as you have propane and you run the furnace, there should be no problem.
On the flip side I can keep my trailer at 64 degrees in 115 AZ heat in the full sun.