This is what I made / use. I think I got the original concept here on the buzz. The section below the 4-way is not glued so it comes apart, yet is held in when used. I fill it with Great stuff so I can be assured it will float if needed.
I epoxy and put a screw into the mount so the camera is not likely to get detached.
I had one survive while filming 5 miles of the bottom of the boat on Westwater this spring.
You might want to run a cord from the D-ring to the camera, but I have not found it needed.