When I made my magnetic mount for my go-pro it made it all possible. You always learn interesting stuff from it. Like with the video of my 2 you can really see how much the entire torsion beam moves side to side. I have a bunch from under my Miata as well.
This is basically what I did except I did not sand/file the edge down on the metal cup around the magnet. I only use it under a car so I really don't care about scratches. I don't know why anyone would use it on the paint when a go-pro comes with a good suction cup mount.
Anyway I have had my go-pro for 5 years now so I really don't care about it much, but the mount is really strong and I have never had it come off from under a car no matter how stuff the car is, or how bumpy the roads was.