hy,
if you do like to go skying at those temps I would recommed the bigfoot 3000 rated -40 C with double windows 2 inch insulation 10.5 floor a lot better. had one for 3 month, best camper I,ve saw and probably the best ever built. but is heavier around 5000 lbs you need at least a f550 dually to move that thing...because is so heavy people don't like it and it less money than a 2500 series
other than that you could try a 2 inch foam under the camper, like I did, under the matress 1 inch foam, window plastic screen sold at home depot does a great job in cutting the cold air from windows without adding to much weight. I would to some kind of a removable protective box with a 3-4 inch insulation to cover the dump valve, make a 3 inch hole with a 12V fan to push more hot air from the camper to the valve area. valve area is far on the corner and doesn't get much heat from the camper
some use in rvs olympian catalitic heaters quiet, very efficient to heat the interior and less humidity than regular rv furnace( good for heating the exterior)
no problems with the fridge at those temps? some say the fridge is not working at those temps
incognito