I wouldn't trust just the weld. I don't know how strong that can be, but mistakes always seem to creap in...
There is a maker in Texas, Seth Hamon (no, no gaitas, only others), he makes bags from leather, but using a rather unconventional technique. He glues the two sides together, and glues over it a strip of leather. So far conventional. Then he turns the whole thing inside out, and glues a strip of leather onto the seam. This side becomes the outside.
If you squeeze the three above images togather, you get the cross-section of the seam of the eventual bag. The outside is on the top. I think this is worth doing in rubber, too, it is far stronger than just gluing two sides together.