We used solid poly cord in '09 it worked well. Welding it was a bit of pain so we decided to try hollow cord this year. It has been working great. We use 5% strech, it works fine. To keep it in place we simply drilled 2 .250 holes in our Aluminum pipe roller on either side of the cords. We cut a short length of cord and stuffed on end in one hole, wrapped it around the pipe and stuffed the other end in the other hole. It works great, the poly cord stays in place and the short lengths have not slipped out at all.
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Forgive the image, the photo has a bag between the bot and camera
