I believe dual pane makes a huge difference in extreme temps.
Just picked up a new Arctic Fox 5th wheel to live in 3 days a week here in Gillette, Wyoming.
Just set it up this past Monday, and Friday morning it was -12 degrees. Have the furnace set at 60 degrees, running the fire place, and one electric radiator heater and it's a comfortable 69 degrees. Today it's 15 degrees, so far no fogging, and if you place your hands near the windows, you feel no cold radiating from the windows. I thinks the double panes, and having it skirted makes all the difference.
BTW, the unit came with the dual panes and a 6 point leveling system, and coming from a unit with single panes, and no leveling system, I wouldn't be without either.