this lite-craft pop up has a pvc tarpaulin material outer, and inner, and an additional synthetic insulation in the walls. so the flex pop up walls have good insulation.
the key however in the cold conditions is the need for a good furnace that runs reliably, and a good 12v battery for the fan (the solar keeps this battery charged). and you need to let the furnace run. this keeps the water from freezing, and comfortable. i was hunting in 8 deg temps, and any camper will get cold, and will freeze if you do not have a furnace running.
i feel like the walls and roof are good. the areas the coldest are the wood floor, and wood structure in the bottom of the camper, and in contact with the steel bed. This area could benefit from some dense rigid insulation.