I made a camera mount myself too. Here is what it looks like:
I bought a swivel ball camera mount (from Amazon) and installed it on the end. I drilled a few holes at the end of the "C" so I could move the position of the camera around. I always leave it on the end though. Make sure you use some washer (sping type) otherwise you get some wierd metalic noises while you drive. I still have not eleminated all those noises though. I used some "C" shaped brackets I found at my local hardware store - they use them on the ends of a step ladder. I used an extra "C" clamp for the other "bar" to use two long bolts to clamp the camera mount down on the headrest posts.
Holes are:
9.5cm apart. (Btw... there is still room to spare with the bolt holes at 9.5cm's)
Back bracket is:
23cm long
Bolts are:
M8 and 75mm long
Here are some of the video I have shot this way...
Driving around in Germany (videos inside!) autobahn driving…
http://www.1addicts.com/forums/showthread.php?t=424388
Dackel