Still not a whole lot of spare time to work on this, but I managed to get the ply boards screwed down to the support structure this afternoon. Unfortunately, one of the ply boards was a bit crumbly (the last piece before the old door), and they ended up not being as pliable when screwing them down as I expected based on earlier tests. Also, roll tests with a ball indicate the run 'groove' may still get dangerously high on the curve near the end.