I mounted mine on the top rear of the cage. I mounted it to the base of my whip mount. Its great for when you are following because the field of view is big, but since its high up it is hard to see things like big whoops or how steep hills are. My son rode with me and held it in his hand on one ride. He put it out the side at tire level and it was pretty cool to see that view. I may try to figure a way to mount it like that. Here is a view from my current mount location.
I welded a tab to the top bar on the back of the cage for my whip. I use a Tribal LED whip and the mount it came with and I used the GoPro cage mount to mount it to the actual whip mount since I could not find a 2" GoPro cage mount. I will snap a pic of it when I get home today.