Thanks Jeff,
The plastic came from a local shop that sells outdoor materials/notions; cordura's, wax canvas, pack cloth, buckles, webbing, hook and loop etc.. I can't for the life of me remember what it's called. They use it to make windows and things for outdoor tarps and things of that nature. It's a bit rubbery feeling almost, not rigid at all.
It sews fine with the gros grain at the edges. I wouldn't sew it to itself as it would likely rip tear at the needle holes.
The mount is actually the simplest part of the whole thing. Holes are drilled through the mount to use zip ties to attach to the bike. 1 zip tie around the stem, 2 around the bars. Just line up, measure and mark before you drill your holes to get the spacing between stem and bars right and so that you don't drill through any of your stitch lines. After I posted I realized the mount was photographed upside down...the stem holes are up the bar holes are on the bottom.
http://www.bikepacking.net/forum/index.php?topic=5347.msg44117#msg441174th and 5th post in that thread. 2 different trips on two different set ups.
Simple design but very effective, and the map case is removable so when you stop for a break you can just tear it off and have a look, reposition it etc..
