The Oldtown kit is way overpriced. A poly resin is ok but an epoxy resin is going to be a little more forgiving. Heating it with a torch or heat gun is just to help bring the mold release agents to the surface. That's the biggest problem in getting a repair to stick. The surface has to be extremely clean. So heating it to bring them to the surface and then using a quality cleaner to remove them is your best option.
Plastic welding is another good option. There are some better products out there than using a milk jug, but I've seen it used on a bumper repair and it turned out nice in the end.
There are also some other products used for bumper repair that would work probably the easiest. It's a two part product that takes a special applicator gun. You still need a clean surface and you will still want to use some cloth to give it strength. I have an applicator gun, enough cloth to do 3 or 4 complete canoes and can probably get my hands on the material you need for an awesome price. You know where to find me.