So I have used some Scotty plastics (mainly aimed at fishing) stuff for a pole camera mount on my mini-cat for a couple years and I most recently just picked up there Float tube strap mount for a back of Raft Camera mount for R2ing in a buddies raft. I just wanted to post some pictures of the set up as it's off the shelf essentially, no fabrication required, and it's good quality. Note you could replace the black straps with plastic buckle that come with it with cam straps but they seem ok for now - we tested them out and all that. Doesn't seem to move with enough tension on the straps but if you flipped and the pole hit something it should slide/move so I think it's just the right amount of tension if it's fair to say to hold it in place. Here are some pics of the set up. Can also be strapped around a thwart for more of an upfront view.
Here is a list of the products used in this picture (No association to Scotty other than my name is Scott LOL)
No. 241 side/deck mount
No. 254 Rod holder extender (optional to install to raise camera mount up)
No. 135 Camera/Compass mount. Has a slot to hold Go-Pros and a bolt that is the same as most action camera tripod mount threads
No. 266 Float tube Adaptor
If you use a little black electrical tape (the joints do lock together) it helps snug everything up together better.
Looking forward to getting some sweet video using this set up.