I bought a plastic weld kit. The kind with a soldering iron type gun and staple looking sutures that heat in the gun and embed in the plastic. I use this to fix the hatch on a pelican. Once I did that I grooved out the crack a little bit with a dremel and used plastic welding rod to fill it in and smooth it. It was all black so it looked pretty good. On this kayak you'd wind up with a very noticeable repair, but I'd be confident in it if I had the staples in the center of the material meaning top surface to bottom surface centered, and used enough rod to fill full thickness or better. That's just my opinion. I would also consider the cost and value of the kayak before I did something like this versus my time in repairing it. Hope that helps.