What nobody so far has mentioned is construction. Modern campers are mostly aluminum framing. Over the years, we have had three truck campers. By far the warmest and most comfortable is our current camper --- and its a pop-up! But it has wood framing, not aluminum.
An aluminum frame sucks in the cold and dissipates the heat to the outside. The aluminum also contributes to condensation both inside and out. Aluminum transfers heat really well. That's why it's used for heat sinks. Wood is a vastly better thermal insulator and makes for a warmer dryer camper.
I never thought I would be a fan of wood framed campers. But I am. They are simply marvelous in cold weather.
