A couple of single cups might work pretty well. As long as your boom and your camera aren't very heavy (and as long as you keep the driving speeds reasonable), you shouldn't need too much suction power. With the two double-suction handles attached to the boom, it felt very very securely attached to the car. There weren't many mounting options though because the car has a lot more curves than it seems at first glance. Using some single-cup handles might give you more flexibility in mounting it too.
I don't think I ever got any decent pics of the whole mount. I threw it on that one day and then kind of abandoned it after that because it was just too shaky. It seems like it really needs something to triangulate it for stability, and the more ideas that I came up with the more expensive it looked like it was going to be. It seems like it would actually work pretty well for a photo boom shot, because it didn't shake too badly at very low speeds, but even at speeds under 30mph through my neighborhood it started to get too bumpy for my liking.
Parts and assembly was pretty much as follows:
- 2x double suction cup handles from Harbor Frieght
- 2x conduit hangers (1.25" or 1", can't remember which)
- 3x 1/4" bolts
- 2x 1/4" nuts
- 1x ball mount for camera
- 1x long scrap aluminum square tube
Attach clamps around each suction handle.
Drill holes in bar and insert bolt through clamps and bar wherever desired.
Secure with nuts.
Drill end of bar, attach ball mount to bar with bolt.
Find large flat surface to attach suction cups to.
Mount camera on boom.
Try it out!