I like the idea, and that you’re careful and ecologically conscious about the choice of material 
I don’t know anything about surfing and the requirements for a good surf board, so not sure if the proposal makes any sense but recycled plastic could be another durable and lightweight raw material. (The question is of course how to make this durable. But that’s something to explore, as in “the artist is the one who limits their choice of tools and then masters those she chooses”.)
Whatever technique you choose, no need to squeeze the project into a week. I think we have enough capacity in the house for longer stays, as long as needed.