I made this for a friend who was going snorkeling.
We tossed around some ideas of how to make an underwater hand held monopod for his GoPro dive housing. However, it can be used for any application where a hand held GoPro camera is required.

Step 1: Materials

I wanted to limit the materials to as much plastic as possible so as to avoid corrosion from salt water.
Originally I was just going to make a simple, short hand-held grip for the camera, but found some PVC fittings that would allow for a cheap and easy extension section.

Basic materials are PVC conduit (electrical) and fittings and Lexan

3/4" schedule 40 PVC conduit left over from previous project (surf fishing cart). Cheap from Home Depot (HD). I used a short length for the hand grip and cut a longer section for an extension section.
.093" thick Lexan (polycarbonate) sheet left over from previous projects (motorcycle wind deflectors). 8" x 10" sheet $4 at HD
3/4" threaded conduit fittings - (2) male and (2) female - less than $.40 each
3/4" pipe cap (from plumbing section, that's why it is white) - less than $.40

Step 2: Camera Mount Prongs

Originally I was simply going to screw a GoPro tripod mount to a 1/4" machine screw at the end of the hand held monopod.
The I realized that a mount similar to the standard 3-prong GoPro mounting system would be better.
I was going to make the 3 prongs out of thin aluminum bar filed to the proper thickness, however, I realized the aluminum would corrode in salt water and thought of the Lexan material.

The .093" Lexan is similar in thickness to the outer 2 prongs, but thinner than the inner prong. 2 thicknesses of Lexan are thicker than the inner prong, so I decided to glue two section together and then file them down to the proper thickness.

I cut (4) 1/2" wide x approx. 4" lengths of Lexan to make the 3 prongs.
I glues two pieces together with superglue and clamped it in a vice for about 10 minutes. (Remove protective cover from Lexan before gluing together)
I drilled two (7/32") holes through the stacked and aligned Lexan pieces.
Next I screwed these together with #10 machine screws. These are the same size as the GoPro mount screw.
Next I sanded the pieces on a drum sander in my drill press to round off the top and narrow the pieces to match the standard GoPro mount dimensions.
Lastly I sanded the middle prong (the glued up double-thickness Lexan) to reduce the thickness to match the standard GoPro mount. I sanded both sides equally which you will see why later.
This could also be done by other power sanders, or by hand on sandpaper or with a file or combination of the two.
Drill a 7/32" hole in the opposite ends of the Lexan pieces before you cut the prongs down to size. Cut pieces to required length (see later step for how they are assembled and figure it out). Save the cut-offs with the holes for the next step.

Step 3: Assemble Camera Mount

The Lexan prongs will be assembled into the end of one of the 3/4" PVC female threaded fittings.

First step is to drill a 7/32" hole through the slip-on end of the female fitting. The distance the hole is back from the end of the fitting is determined by the placement of the prongs into the fitting.

Next, assemble the 3 Lexan prongs onto a standard GoPro mount to set up spacing. Cut two small lexan shims with 7/32" holes in them from the scraps you cut of the end of the prongs. Place two the spacers between the 3 prongs and tighten down on the GoPro mount screw to help hold everything in place.

Next, carefully insert the bottom of the prongs into the PVC fitting and insert a #10 x 1 1/2" stainless steel machine screw and nut through the holes in the fitting to hold everything in place. It will fit loosely, but that is OK for now.

I used plumbers putty to secure the prongs in place. There are many similar products on the market, such as JB Weld. Any type of two-part epoxy plumbing putty should work. Knead the putty together per the manufacturers instructions and force it into the fitting in and around the prongs. Use small tools to pack the epoxy into all the gaps and do the same from teh underside, being careful not to get the putty into moving parts of the GoPro mount or into the threads of the fitting. If you do, scrape it out before it cures.

When everything sets, the prongs will be properly secured. While the putty is supposed to hold to PVC, the machine screw will ensure the entire putty mass does not pop out of the fitting.

Step 4: Assembly

Assembly the hand-held section:
Slip one of the PVC male threaded fittings onto the small length of PVC conduit and screw the new mount to the end.
Put the cap on the other end.
Not shown - Drill a hole in the cap and thread a loop of paracord through for a wrist strap. Add a spring-loaded cord lock for adjustment
Optional - Add handle material to the conduit section. Didn't find a material for this yet, as it was a one-hour project that I had to turn over quickly.

Slip the other male and female threaded fittings on opposite ends of another piece of PVC conduit (lengths as you like) and use this as the extension piece.

Glue all fittings to the PVC conduit sections with PVC Conduit Cement. I would add a thorugh machine screw to ensure that if the cement bond breaks, the fitting stays on the end of the conduit section.

My friend chose to leave the glue off and instead used machine screws and wing nuts to easily break down the monopod and components for traveling.

Step 5: A Slightly Different Version for Myself

Now that I am going snorkeling, I made a slightly modified version for myself.
This one uses 1/2" PVC pipe because the outside diameter was about the same as the 7/8" ID bicycle grip I had for the handle.
Materials included: