Update 20180614: v4 is here: https://www.youmagine.com/designs/action-camera-diver-s-handle-4-aussieland-edition

Check out 2nd version of diver handle here: https://www.youmagine.com/designs/gopro-diver-s-handle-v2

I made two spikes which can be screwed into the bottom of the handle to fix the handle into the sea bottom and record sea eels. The spikes can be screwed into the grips too to raise the camera from the sea bottom. You can also store them in the grips if you turn them in reversed.

Layer height = 0.1 mm.
100% infill = spikes, mount, grips. Note: the mount does not require support but you have to clean the edges.
20% infill = left & right holder parts.

I made the entire model in a more-or-less easy to read openSCAD script so you can easy fit the model dimensions to your need. I also separated the GoPro mount creation script to a single module to help reusing it in other projects.

To assemble the handle you will need two 25 mm M5 stainless steel bolts and two M5 nuts. If you prefer imperial sizes you can change it in the script and re-render the holders and the mount.