Insulation

We camped several times in single-digit temps (not by choice, but because we were heading either to FL or back to MI in the dead of winter) in both our Class C and our 5er - and we stayed comfortable. I covered all the windows with Reflectix (like bubble wrap with foil on each side) insulation cut to fit so the shades could still be lowered; and we put those foam/fleece "vent pillows" in all the overhead vents. Close the ducted A/C vents and put a layer of Saran Wrap over the A/C grill - and you're good to go. IN our case, an electric heater did most of the work, and the furnace would kick on, on occasion. The only thing we didn't do at 5 degrees above zero: use the water or toilet. Our plumbing was mostly-contained inside the bottom shroud; but the water drain, and dump valves were exposed.