Our coach also suffers from being very cold up front when the weather is below freezing. There's just so much glass, etc., and our furnace's most forward vent is still some 4' behind the passenger's seat. We also have some single-pane windows in our slide/
We travel with the LP furnace on, the generator on, and 2 1500 watt electric heaters to maintain a 'shirtsleeve' environment that is nice and toasty (about 72F). We also have an extension cord and a 3rd 1500 watt heater if things got really cold (probably below 10F). I'd start to be concerned about water lines in an extended freezing drive, though, but that's my particular coach.
The Green Machine -- 2000 Mountain High Coachworks Summit (Spartan chassis / Cummins ISC)
...and F-Troop: Fearghus, Fiona, and Frankie (Cairn Terriers)