I use a 6db omni suction cupped to the top of my car. The mirror effect of the metal of the roof should bring it to 9db. It is very nice not having to give my wrist RSI, and still have superior "resolving" power.
I'm building (yes, building) a ~250mW bidi amp for wardriving. Too bad I blew out the paired amp dots... now I need to buy a new set.