Great find on the wrinkles! It does make sense that it could be rolled for easy storage. It might also explain those strange "floorboards" we see in TMP during one scene, since they might well be the actual floor!
I found a picture in my "Making of Phase 2" book that might be interesting:
The FP disc segments are clearly seen, diminishing in size as the tube goes on. What's interesting is that the "crystal" segments do not diminish in length (nor are they built beyond a simple connecting rod, since they were never going to be seen on screen.
The backdrop painted is set up and ready, and I do wonder if the idea was ever toyed with of extending the tube even further by included it on the painting. This really would have increased the size and scope of the Engine Room a lot more!
The "real life" length of the horizontal tube can now be estimated more easily, if required - there are 10 FP segments and 3 full size segments - 13 in all, plus the conical junction to the vertical tube.
If each horizontal segment is about 4' in length then the overall length of the tube would be 52'
YMMV, of course