Saw this and thought it was pretty cool. Talk about maneuverable..... Might be better suited for another forum, but wanted to share with all of you... Click here.
I think the main problem would be the connection point to the car. Roof gutters will not provide enough support. It is a cool idea, but the entire roof structure would have to be modified. Not sure how that would be done.
Look at the connection points in a truck for a fifth wheel. Very beefy. Sheet metal will not provide enough support.
I know, buzz kill. Sorry, but that is probably why it never took off.