Find the IN end of your NeoPixel strip - it is the end with the arrows pointing away, down the strip. If your strip already has wires connected, trim off any connectors, and trim off any additional power wires that might come pre-soldered. You want a black wire, a white wire, and a red wire remaining.
Lay out your strip around the perimeter of your snowboard on its edge with the lights facing outwards. Cut the strip to the desired length, cutting carefully between the copper pads.
Solder a red wire and a black wire to the +5v and G pads on the OUT end of the strip.
Slide a piece of 3/4" clear heat shrink over each end of the pixel strip. Fill the heat shrink with hot glue, then while the glue is still wet, shrink the heat shrink with a heat gun. This will encase the wire connections in solid plastic, waterproofing your strip and keeping the connections safe.
Starting at the middle of the board between the bindings, lay a bead of silicone glue about 1/4" from the edge of the board. Don't get too close to the edge, or the snow will pull the LEDs right off.
Glue your pixels to the board as shown, starting between the bindings and lining the edge of the board with the pixels facing outward. This will give you the most visibility and illuminate the snow as you glide over it.
Clean off any excess glue with 99% alcohol before it dries.
Strip some shielding off your wires. Twist the two red wires together and the two black wires together. We'll connect power and ground to both ends of the strip to help distribute power evenly along the pixels and to add a bit of robust-ness -- if any one of these four wires fails, the board will still light up.
Find the male half of your waterproof connector and slip the included silicone gasket into place.
Slip on another piece of 3/4" clear heat shrink, and also slide a piece of heat shrink onto the red, black, and white wires.
Solder both of the red wires from the pixel strip to the red wire on the connector, and both black wires to the black connector wire. Solder the white wire from the IN end of the strip to the connector's white wire.
Plug your connector into your GoPro case setup and test to be sure everything works. Once it's all solid, waterproof this connection in the same way you did the pixels, filling the 3/4" clear heat shrink with hot glue to make a solid plastic encasement for your connection.
Add some more silicone glue to secure the wire bundle to the board behind the NeoPixel strip.
Initially I mounted the GoPro case directly to the board using the GoPro mount hardware that came with the case. After a few trial runs, I discovered that the electronics and battery seemed to get too cold being that close to the snow.