Thanks. We've found the Elwell electric element does a good job heating the trailer down to the mid-40s. Anything below that requires either the Elwell diesel burner (not the hot water) or the under-bed diesel heater. It seems the under-bed is more fuel efficient...
Did you use both the diesel burner (lower left Elwell icon) and hot water options (upper left Elwell icon), or just the burner? I think you ran the Elwell while traveling as well...which heating options did you use while driving?
I literally just picked it up today from having a bunch of mods done. We took delivery 1/24 and drove it 3 miles to the shop. I put about 80 miles on it today...so far, it rides pretty well considering it's such a beast. I think you'll be happy with yours.
The filter is mounted to the exterior underside of the trailer, so even though it's wrapped in foam insulation it's still exposed to the exterior ambient temperature. That's why prolonged exposure to sub-freezing temps "could" be a problem...
Even leaving the foam in place and wrapping it with...
Maybe check out a Kimberley Kamper. Probably more canvas than you were thinking, but you're living in a world of compromise with your use case. Literally a 30 second setup, so that might offset the canvas concern.