We've been working on a short during the summer which you people have indirectly contributed to by helping me with a lot of questions. Thank you all for your help!
I'm kind of hoping to return the favor. We have one scene where the talents are driving an old Mercedes and having a bit of dialogue going on. We tried shooting the scene from the back of another car during our first filming session, with bad results. The picture was shaky, and worst of all, the reflections made it impossible to see through the windshield.
We're reshooting in a couple of weeks. We had to come up with a solution.
We came up with this monster:

Side view:

I studied some professional models and the only thing that kept me back was the price. I simply couldn't afford the real ones, so I had to find out some other way of doing it.
The suction parts are used for carrying glass and can according to the manufacturer withstand weights of up to 100 kilograms (220 pounds) each. The rest of the stuff was bought from a very cheap construction market called "Biltema" ( the Ikea of all stuff mechanical ). The only actual camera part is from Manfrotto/Bogen(part 293) and I was lucky enough to get a showcase leftover version for 30€(~37 dollars). Total costs for the thing are somewhere around 60€ (~75 bucks).
It's steady, at least when the mattebox is removed. We also got a circular polarizing filter to get rid of the reflections. This will hopefully solve our problems with the scene.
Here are a few pictures with all the extra straps, batteries and plugs removed. It's a bit easier to distinguish the construction:


The only tools needed were a pair of wrenches, a screwdriver and scissors.
Hope this helps someone, comments on refining the construction and critique is always welcome.
Mikael.