The following is where I bought my laptop mount system and for a small fraction of the price the others cost. I mounted it to the floor by unscrewing the front inside bolt of the passenger seat, slipping the predrilled floor flange that comes with the mount system under it, and then tightening the bolt back down. It's solid as a rock.
Also, the mount comes with a quick disconnect, which allows you to remove the stand when not in use without having to unscrew the bolt in order to remove the flange.
http://www.mobilelaptopmount.com/