as for camera mount. a regular 1/4" bolt has the right threads for the bottom of the camera. i also put a wing nut upside down on it to snug up to the camera to hold it in place (And so i dont have to bottom the bolt out) not shown in the picture
I bought THIS from Amazon. It was the cheapest suction cup mount I can find. It works inside and outside the car and is pretty solid. The only problem, if you mount it on the inside of your windshield, like I do, you have to edit the videos and flip them 180 degrees because there's really no way of mounting a camera right side up at the angle of a Focus windshield. But for $18, you can't beat it.
i made mine out of pvc pipe and some u bolts, got a suction cup mount to rob the little nut to hold the camera on and was golden. my thread in here has a picture of what it looks like if you need more pics let me know ill take some
I use a similar headrest mount, but I then use a ratchet strap to snug it down. I fold down the rear seats and hook the ends of the ratchet strap to the loops that the rear seat clicks onto, this helps emliminate a lot of the seat shake. I also push the seat all the way back so that the passenger seat back makes contact with the rear seat that is folded up, this also helps to secure the seat and prevent it from shaking.