TBD
Plan is to make 4 structures of a light aluminum beam structure and just fasten 3-4 layers of XPE - Sleeping mat on it. The 4 structures should fit the area between walls/the slider and be detachable. On the from area Ill add the same 3-4 layers of XPE - Sleeping mat.

This is the structure to keep the middle plastic sheets and a side door in place. It is fasten to the front aluminum 20x20 arch and will cover the back area when the wagon is "pushed together" (rolling/running/walking mode) the idea is that the space between back and fron skeleton should be about 25-30mm later the plan is to fasten PVC U shape 20x20 beams on each side e.g. on the back inner part of the middle part (outer skeleton) and on the front outer part of of the back (inner skeleton when in rolling mode) making the two U shape inter lock in a S shape when wagon is opened in "sleeping mode" forming a weather barrier.

PVC L shape 30x20x3mm beams are used they are more sturdier then the 30X30x2 I used before and weight the same. I might rebuild the inner skeleton with this also.

One set of beam was fasten to the aluminum 20x20 arch on each side, and two more was fasten to form an big rectangle and fasten in each corner with M4 screws. NOTE By putting the screws a bit closer to the inner corner it will make the structure possible to fold together nicely, I used 12mm instead of the middle 15mm. You also need to trim off the corner that are in the way when folding.

On the back part of the slider a small "flat" PVC part was fasten in the last screw just big enough so the back part of the skeleton can be fasten in it in the "right spot". E.g. the skeleton is fasten in the part of the sliders that will end up in the front when opened, together with the compleat front. So when slided out the front and the middle skeleton will slite "out" over/from the back part. e.g. instead of opening a drawer you will slide out the cover.