These trailers are much warmer with the slides in.
We travel with the sides in all the time Ha ha ha
Not with this one but in the past we always left in the winter and the furnace with the slides in will heat it much faster enough to heat the bedroom a little more and the rest gets warm to.
As long as the furnace is running when parked it should heat enough to prevent freezing inside, because our water in jugs never frooze.
I remember reading my thermostat one night it had gone down to -20F in Maine while driving south and we were warm as toast in the bedroom.
Always leave your trailer winterized and do not fill the tanks till its warm enough. We used the jugs to flush the toilet and the black tank never did freeze if only used during the night.
When winterizing I use to pour windshield washer liquid in the black tank to seal the 3" valve against freezing.
Better have lots of battery power (2 min) because the furnace in our BC will kill the power fast, but if only stop for an 8HR sleep after traveling all day they should be ok. I have 10 Ga wires to the trailer connection and the truck charges at 23 Amps to the trailer batteries.
The original 16Ga wiring on my truck to trailer connection was not doing much, so I installed a better one. It takes a long time to recharge these batteries after the furnace has killed them.