I have known folks to use Azek decking. I believe it is a PVC based material. You have to go to a lumberyard, and they will probably have samples for you to look at. If I remember correctly, Rosewood and Cypress were two colors that might work. I have found white Azek trim in the big blue and orange box stores, but never the colored decking material. I have heard of people using Trex. I believe Trex is wood fibers encapsulated in polyethylene, and based on what I saw on a few TV shows, it's often recycled plastic grocery bags. Personally, if I wanted to replace wood on a boat, the LAST thing I would use would be any kind of wood fibers, encapsulated or not.