Thanks for posting this. How did you attached the GoPro3 top and bottom to haul it up the mast? I've tried this but not successfully as you.
I had a small plate of stainless steel lying around (something like 15cm x 10cm) and fitted the GoPro stick on base. I had to tape up the plate to protect the sail.
Perhaps what helped the most is that I had a halyard mounted on the outside of the mast for the passerelle that I dont use any more. Because the block is mounted to the side of the mast it meant that the SS plate sat flush with the mast.
I can imagine that it would move around much more if I had used a normal halyard.