I recently bought a super tiny camera for FPV off amazon (which is actually really impressively good!) and it's so small that there wasn't even a way to mount it. I created this case which snaps over and has wire feedthroughs for the signal wires. It's also got an M3 sized hole to mount with a screw.
The case has the equivalent of a lens hood to keep the camera lens safe in the event of a crash or collision.
Here's the cam it works with (it comes under tons of names): http://jay-greco.com/images/516Xa0pBjGL.jpg
Print flat side down so it builds the half-circles upwards.