There's this thing. The Sealtite(tm) that you can get at Wal-Mart. It's supposed to be used to reseal things like bags of chips/cereal and such.
I picked one up and was messing around with it. The thing takes 2 AA batteries, and basically heats up a little wire to glowing hot when you press it closed. I noticed on some of the forums that some folk like to melt the cuts they make in silnylon and other tarp/hammock materials.
I was wondering if anyone has tried something like this to weld hems and seams.
It appears to weaken the material a little bit where it's used, depending on how fast you pull it along the seam. If you pull too slowly it acts like a cutter, welding the cut as it goes, if you pull to fast it doesn't melt it at all.