You bring up some very valid points about the insulation limitations inherent in Campsters. Please let me know what you think about this plan. (I hope I'm not on a fool's errand!)
I'm going to take apart the panel under the fiberglass pop-top and insulate it too. Then, when the weather reaches my "cold tolerance" (or intolerance, as the case may be), I'm going to lower the pop-top so the uninsulated boot will no longer be an issue.
The floor is another thing. . . I'm going to use a layer of the "hot-rod" insulation on the floor and then cover it with those foam tiles used in workshops. They're like 12 x12' ensolite tiles. Finally, I'll put the rolled vinyl flooring on top of that. By the time I'm done everything will be insulated except the door. As for the seals, well, I'm open to suggestions!