I was not satisfied with what was offered as far as mounting a GoPro on a DSLR body. After about 15 failed prints, I decided to model my own.
I have added rafts and supports which help make a clean print, however it will require some cleanup post print. I used .25mm Layer with 50% in fill on my Rep. 2X in Black ABS, but I'm sure other settings (as long as its medium or fine) may work as well. It fits snug on the hotshoe with no rocking and the Gopro Mounts like butter.
Solidworks, A Canon 5D Mk2, a Gopro Hero3 and a set of calipers.