almost any plastics place will be able to supply "teflon" (it is NOT teflon) in long lengths, but it is not cheap, if you go that way, make sure you explain to the shop what you want the plastic for and they can supply the correct material, the blue and red stuff you get from boat shops (with the "slot" for screws/rivets) comes from over seas in the 1.5M cut lengths, I doubt they could order in any other size, unless it was a big volume order. The weight of the boat should indeed be taken by the centre rollers/skids/whatever, the side "bunks" are to stop the boat tipping over, thats all, and the tension put on a hull by a wide ratchet tie down is extreme, make no mistake about that!