Ok, so I know there are lots of good cheap plans out there to make all kinds of different boats, and I do plan on making some. But I occasionally like to do something different. Something off the wall. So, here's my idea. Schedule 80 PVC frame. Duct tape outer skin (it just comes in so many pretty colors, very strong, and according to Mythbusters, you can make a boat out of it. Flex Seal rubber spray coating stuff (As seen on TV, you can make a boat out of it lol) for the inside of the duct tape. Then, for added strength, great stuff expanding foam for the inside layer. If you can get it somewhat uniform, it should make for a good inside for the boat. Probably sandable and paintable. After all this, it should be VERY lightweight and watertight. Just a random idea going through my head, wanted to see what your thoughts were.