I dry camp the TT up in the mountains here in Washington each October for Elk season.
It gets down to the upper 20's at night.
I have never had an issue with frozen water or drain lines. At night I put the furnace on 50* and also run a catalytic heater, a small one that runs on the small propane bottles.
Each morning I turn the furnace up to knock the chill out of the air for breakfast.
Recharge batteries about every other day.
My other hunting partner leaves a burner on the stove lite on low all nite in his RV. I keep tell'un him he's go'un to wake up dead if he keeps it up. Every now and then his carbon monoxide detector does off
Lee