I also saved money.
Very easy and inexpensive and customizable to whatever backpack you use.
Video of the finished product in use can be found here:
Step 1: Materials
3/4" wide Velcro
Small machine screws, washers and nuts
1/4"-20 short machine screw
GoPro tripod mount
Step 2: Mounting Plate
It's available at Home Depot and pretty inexpensive ($4 for a 10" x 8" piece).
I used a piece about 4 1/2" x 3 1/2"
Cut the top two corners off on an angle to suit the strap locations.
Mark 4 slots in the 4 corners where the 3/4" Velcro straps will attach,
Angle the top slots to match the cut corners.
Drill a small hole at the end of each marked slot and cut between the drilled holes with a coping saw to complete the slots
Drill a 1/4" hole in the center for the 1/4"-20 thread tripod camera mount screw.
Drill a hole between the bottom slots to suit one of the small machine screws. Locate the hole close to one slot
Step 3: Straps
Use a washer against the Velcro and one against the Lexan.
Run a length of Velcro through each of the upper slots, double back over a short distance and make a hole for a machine screw. use a washer at each side of the Velcro.