I'm not a regular mobile CW op--I tried it for a while, and it's worlds of fun, but the traffic where I live is too heavy for me to be comfortable with running CW from the car.
My regular Benchers were too heavy to be convenient in the car. I tried my homebrew paddles in the car ( http://people.duke.edu/~kuzen001/mousetrap3.html
) but the action was a little bit light for my taste.
I wound up making most of my mobile CW contacts with a really ugly sideswiper, an old cheap imitation of the Vibroplex single-lever model. I bought it cheap at a hamfest, and it has a plastic base, so it was light and easy to mount in the car.
Whatever you wind up with, GL and please be careful! :-)