I have always thought...

Great stackable shelves could be made from wood pallets. There are allot of videos on YouTube about how to break them apart.

I think you could use wood with the plastic screwed to the wood for the boat. You would have to bend the wood, but that's very doable. Gorilla glue may work in addition to the screws or maybe even hot glue? All the glue really has to do is keep the water out and hot glue might melt itself into the plastic and it's cheap... Hmmm, the problem now is I already bought wood, lol. But... I need to experiment with bending wood using my heat gun. You get the wood formed right and it's just about got to work.