As a warning. A BIG varningslarm :P
In the event of a collision, this has the capability of causing severe personal injury. If you have active headrests, this will likely interfere with their operation. If your bar extends too close to the B pillars, side impact air bag (especially the type built into the seat) operation could be compromised. So please, take note of this.
I made a similar mount for a friend (this one is for myself). He likes taking pictures of and in his car. Soooo, I'm making him a suitable mount so he can take pictures from a stable location while moving. Long exposure + night time on highway = really cool effect ;)
Step 1: Materials
4 Screws of your choice
4 Nuts to match screws
1 piece of angle iron OR aluminum to span your headrests
1 Screw to fit your camera or swivel mount
Optional: Screw Caps
Step 2: Assembly
Sand the edges of your rod to prevent cuts and scratches. Then, for ferrous metals apply nice coat of flat black -- or even textured paint to give it a nice professional looking finish. I used aluminum, and I like how it looks as-is.