I do not have any first-hand experience with foldables. I only mention Yost because the site shows them and some details of the building and construction--I thought this might be helpful, no matter whose design you choose.
Also, I would not be shy about using aluminum around salt water. It is probably important to get the correct "grade" and not mix other metals with it. After all, there is a huge marine boat building industry that builds in nothing but aluminum.