FF, I have no experience with it myself, but you can get "handlebar" mounts for the GoPro line of cameras, which are originally intended to mount the camera on bicycles. I think they come in two sizes (diameters) and one of those might just fit an exterior tube on your aircraft somewhere.
For more permanent uses, you can use the quick-release mounts that come as standard with the GoPro, and attach with the (included) very strong double-sided 3M tape. Leave the quick-release on the aircraft, and snap the mount with the camera into it when needed. There are also screw-on quick-release mounts available,
AFAIK. I know a guy whose Europa is positively littered with GoPro quick-release mounts. (Okay, that's exaggeration, but he must have at least three on the exterior alone.) He uses the double-sided-tape ones and I don't think any of them has come loose in three years of flying with them.
We've also had great success with the suction cup mount on composite gliders (wingtip, elevator and turtle deck) and the (composite) wingtip of a DR400. Although with the DR400 we backed it up with some duct tape.