Here's a vid that v6focus made. He took a piece of PVC pipe (I think) and drilled holes it for each of the headrests to fit down into so it sits right in between the seats. It's kinda ghetto looking but it works!
if you make the seat mount attatch it to the drivers seat so it doesnt vibrate. with noone in the passenger seat the seatback can move around a little.
also, place something between the camera and mount to absorbe vibration or thats all youll hear in the sound. rubber and such works great
I was inspired by WD40's camera mount, so I built my own using supplies from Ace hardware. I'll take a picture of the mount and post it up later today, but here's a video I made using it. It was very bright outside that day, so the video is washed out outside of the car. I'll have to watch the contrast setting on the camera next time.
I got the swivel mount from a camera shop in Vernon Hills IL. It has a quick release and a bubble level. Cost about $35, but with one flick of the lever, you can take the camera out of the mount. To put it back in, just snap it into place.