Our simple rig was made with code 40 PVC pipe. In the drawing below, the GoPro has been rotated 90 degrees around the axis of the pole for clarity.
The length of the rig just needs to be long enough to get under the boat when lowered into the water at an angle. The two one-foot lengths of pipe are used as handles to steer the camera in the general direction of the action. The tee and end-caps were glued using normal PVC solvent type glue. One problem I encountered was that as I tried to put on the last cap, the compression of the air inside tried to push the cap back off. I had to hold the cap on tight until the glue set up. The next time I do this I'll put a threaded coupling on the end of the handle, then seal it with a threaded cap.
We were concerned that the GoPro camera might somehow come loose from the clamp during operation. We weren't using the camera'a the float so I had visions of the camera dropping 70 fathoms to the seabed, so we tied the camera to the pole with string. The next concern was what would happen if we dropped the rig in the water. We didn't have time to test it to see if it floated so I tied a rope to it then tied the other end of the rope to a cleat on the boat. Next trip, if we find it doesn't float, the solution may be to wrap the pipe with a "noodle" pool toy. Not only would this increase buoyancy, but it would reduce the sound picked up by the camera when the pole bumps the side of the boat.
