I would strongly encourage building a whitewater kayak out of fiberglass. I am currently constructing a whitewater kayak from a design I created. I am using ash strips over forms to create the shape. Upon completion I am going to build a fiberglass part that I can paddle. If you are serious about Class IV/V whitewater, as I am, then composite construction is the way to go. Resources for whitewater kayak construction are scarce. Nearly all paddlers on the rivers today buy there boats rather than build them, thus the lack of information regarding construction of whitewater kayaks. Good Luck!!!