Interesting. I was just looking at folding bikes for my 16 and, of course with the latest technology, electric folding bikes are possible (at three times the cost). "Marine grade" folding bikes, like the Dahon Mariner, are pricey to begin with. I thought that the space under the splash well would be a good spot, as the smallest bikes would fit perfect in that space. I've been relocating my batteries and gas tanks with the idea of using that "protected" area (that and getting the boat balanced better). I guess that area is not as well protected as I thought.
Maybe a Sunbrella splash curtain across there would be all that's necessary.
If G.W. has certain items that he wants to keep salt spray off (like electric down riggers), maybe individual covers are the way to go. There is a Cordura fabric that has a fusible plastic backing that allows you to "iron together" the pieces into a waterproof bag rather than sew. I've used that material to make dry bags, etc., and it works great if you can keep the pattern simple.
Mark
"No name yet" CD 16