This looks like a good dash mount for the Prime. I don't have one but I would be curious to see how well it works. I would use it when I have to sit and wait for someone in the car and mount my Prime to watch a movie or something.
http://www.exogear.com/products-exomount-tablet-car-dash-mount.html
http://www.exogear.com/products-exomount-tablet-car-dash-mount.html