I used to go thru at worst, at least a 10 gal tank if temps were 0-20F at a local ski area with a Fleetwood Prowler back in the 90s to early 2000 time frame. one Issue I had, knew problem, did not fix until 9 yrs in, there was a drain Tee that would freeze up and keep water from getting into the bathroom, and from the hot water tank to the kitchen. fter removal, no issues with lack of water any where. My tank was under a couch in the main living area, so no freezing issues.
Being as you have power, having plenty of battery is not an issue. You might want more than a single size 24 that was seems std for power outages. Along with access to a 2500-300wt generator.
We also had the vent covers on the roof. This worked well in snow. except if it was blowing 30-50 mph, then snow came in. Once you had 2-3' on the top, no issues with snow getting in.
no do not use a slide in the out position if you get snow! or at least have many supports under it so it will not sag out, bend etc
As noted, even with the furnace going full time it can get cold. Have crtains etc drawn to keep the warmth in. Single pains with frost over!
also as noted, if reasonably permanant spot, you can put plywood, straw bales etc to make a skirt under to keep it warmer under you to a degree, so you should be warmer above.......
Big issue, i could go home 50 miles away towing the trailer to dry out, warm up, dump the tanks, altho some times it took longest 14 days to melt. Then again, its usually not below freezing in greater seatlle, but we do get a week or two with temps no higher than 32F.....
I would want to be starting the adventure a month or so ago myself, so you are preping in warmer temps etc....
Good luck.
marty