just an idea, but if i'd ever attempt to maken one i'd try to weld or glue the seams instead of sew through them with a needle and make a million holes in the membrane
i'd do it just like the way you repair goretex, hold the two parts together, then glue patch on the outside and a patch on the inside...
for long seems you'd use a sort of g-tex ribbon glued all along the seam....
just my 2cents...
its probably easier than sewing it, if done correctly is quite strong, you'd have less problems with the waterproofing and is easier to repair if they do come loose after time (just re-glue them)
