ScottBaxter got back to me on another forum a week or so ago, and suggested the Sea/Line Kodiak Deck Bag for holding a camera on top of the foredeck. Accordingly, I ordered one and it just came in via parcel post while I was at work. Here is a photo of it. Inside is my Nikon 5500 SLR with the 200-500 mm Nikkor lens mounted. I would not expect it to survive a roll, but on calm days it will preserve preserve the camera and lens against incidental splashes.