I actually take pictures of my mountings (and often post them to the Fly Baby web page) but since I use a Contour camera, they're not necessarily applicable to GoPro users. Aluminum channel and hose clamps, mostly, with foam rubber to harm the paint as little as possible.
Contour has some advantages over GoPro... it's a tube, so there's less drag force on the mount. It also has a rotatable lens, so you can mount the camera on its side and still generate upright video. It uses slide-in slimline mounts that incorporate the standard 1/4" threaded hole for camera mounting. Even has a slot that will accept a bit of safety wire.
Unfortunately, for our uses, the Contour has the same disadvantage of a GoPro: It's TOO light. A heavier device would be more stable, not be as conducive to jiggling, and, most important of all, can benefit from foam and other vibration-absorbing materials. Our little cameras are too light for foam/rubber/other to help.
I've heard the filter helps (it's a GoPro thing, so I'm out of luck). Basic thing is does is make the camera open the aperture more and reduce its frame rate, which minimizes the jellying effect. It's not universally effective, though...many of you probably saw the TV series "Flying Wild Alaska," where they had GoPros mounted outside the Cessnas. You often saw jellying in the images on the show.
I think the only true solution is an image-stabilizing camera. These don't cost much more than the GoPro type, but they're usually a bit larger and hence harder to install. They work by having a bigger focal plane; when steady, the normal-size image has a border of extra detectors. If the image jiggles but still remains on the focal plane, the software corrects the "center point" of the image.
Ron Wanttaja