Erod:
That is the same insulation material that I used to close up the camper. Put it over the sliding window, big window, back window. It does keep it warmer when the top is down. But the pop up "canvas"still loses the most heat. I don't know how well it would work for an arctic pack...hard to fold down me thinks.
I was gonna use some of the leftover and make some insulation for the tie down covers. I note a lot of cool air coming in from them as well. Of course, would leave one open for air, but still it is cold. Also made one for the fantastic fan. I store them on the bed when not in use and have no problems closing the top. Velcro keeps then on.
I think for the canvas, a thin, foldable, insulating material that can form a dead air space is what is needed. I like the idea of felt or fleece or something that can fold down small.....I might make a trip to seattle fabrics next week and see what they might have...
dave