Hey Steve, we take our pop up camper skiing where it can get pretty cold. We have insulation under the bed like Stan mentioned, we use a roll of Reflectix over the pop up fabric along the inside walls as a radiant heat barrier, and we’ve got a 12V mattress pad heater that really does the trick if we turn it on an hour or so before getting in bed. I believe it is made by Electro Warmth (or something like that), it’s marketed for truck drivers, but works great and was not expensive.
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