One consideration is changes in technology. I sit across the room from the large cabinet I made for the 32" tube TV which sits on it and hasn't been turned on in perhaps a year. I wonder if I could just set it on a curb....
I wouldn't make a permanent change to a kayak just for an SLR. (SLR's 60 year technology, kayak 3000 years guess which one we're still going to be using in ten years.)

The huge SLR is on its way out. They're so big because of the mirror and the prism for the viewfinder. Sure we like to see what we're shooting, but as soon as these are eliminated, a camera taking the same quality images is 1/3rd the size.
Basically an SLR compartment should be considered transitional. Maybe a Pelican case attached someplace. Ideally one hand open the box, same hand take out the camera, shoot.

Take a look at the Sony NEX-5 14.2 megapixels, large sensor chip (more important for image quality than megapixels), shoots HD video stereo sound.... It's not waterproof, I don't own one, but it's been clearly the future.

I keep my Mino Hd and little Nikon point and shoot in a Pelican case tucked in the pocket on my spray skirt. It's not one-handed, they aren't waterproof. I haven't had much luck with waterproof cameras, (That Panasonic sounds interesting). I'm interested in the Hero camera.