You may have considered using two GoPro cameras side-by-side for a 3D-rig, but what about a dual GoPro mount so that each can face in opposite directions? This would allow you to capture both a front and back view, and with this rig you can mount your cameras in as a car, snowboard, bicycle, or other items/vehicles. The resulting footage, when stitched together, could be quite interesting.
Although there are certainly many ways to do this, the method below looks like it would work quite well. Made out of aluminum, two J-hook buckles and a pivot arm, it should keep your cameras secure in many different situations.
On the other hand, this design could certainly act as inspiration for other builds. For that matter, the shop seen in the video, with an impressive array of well-organized hand tools could serve as inspiration to update your garage!