I went with a Unden 510 XL which fit perfectly where the ashtray used to be... but that was on a 2nd Gen. Should be similiar on your 3rd Gen.
I got mine from this sight. I purchased a "as new" for a very similar price as seen here:
http://www.unidendirect.com/itemdeta...O510XL&tabid=1
Hard to beat in my opinion.
I also run a 4' Firestick, but had way better reception and broadcasting ability with a Wilson 1000 antenna mounted to the roof. I had mine hard mounted, and broke it off at the base twice in 1 month under low branches... so I am now using the Firestick.
If you go Wilson, you can get a magnetic mount which is fully removable.