In reply to mik82:
I have done extensive mods to packs. Using glue/seam sealer and stitching.
You must have a chunky sewing machine. I have just used hand sewing, or a Speedy Stitcher (like an awl) with conventional strong nylon thread (not the waxed string the Stitcher comes with).
It's hard work, so you have to WANT to do it.