If you were to have any other form of trailer tent or folding camper, it would have a clip on inner tent.
This performs two functions. It's a decorative aid adding colours and possibly patterns while hiding the poles and other such gubbins. The second function is that though light it is in effect a second tent, lessening draughts and providing air gap insulation. Also the bed areas then form into mini tents that reduce the volume of the sleeping areas so lessening the leaching off of warmth into the main tent.
Now I'm not going to suggest improving this with super heavy material, but what came to mind was the very thin silvered material used to line several fabrics.
However at this point I start to have a difficulty describing the product I mean.
At first I thought it was called Thinsulate, but that's just a clever high insulating air trapping fabric.
What I'm looking for is silvered heat reflecting fabric, perhaps something like [You must be registered and logged in to see this link.]
If you try heat reflecting fabric in alibaba you will get lots of options, but does one of you know better than me what I'm thinking about, also do you know how effective it is?
Eureka moment it's like the silvered fabric used for ironing board covers.
Second part of idea: If such a lining were thought to be effective............
I think I'll get your thoughts on the principal before going any further!