Since my last post your roller idea/design has been playing on my mind, I really enjoyed seeing your innovation on this and what you had come up with, that has led me to thinking about it more and wanting to share my thoughts with you, obviously it's up to you if you implement something or not but here goes!

What about if you added a spring to the rollers, milled a slot along their length, then took some thin copper sheet and made some finals for the ends of the belt, so cut to size, fold over and crimp to the belt ends, this strip of copper could then be a sung sliding fit into the recess/slot you made on the rollers, so it would be spring loaded, under tension and want to roll itself back up.

Then you wouldn't need to run the belt through the gantry and would end up using less belt.

Think of a roller blind on a house window, without the draw cord of course.