Get a K40 antenna from Radio Shack a $40.00 Cobra from Wal-Mart will work just as well for you.
I originally started out to do something like this:
but ended up mounting it like this:
and the external speaker is here:
Here's a link to my thread if you want to check it out:
My antenna is mounted with one of Alon's brackets:
'15 RAM 3500 CCLB Dually 4x4
SOLD: '08 F-350 FX4 Lariat CCSB
SOLD:04 Explorer 4x4 4.0
SOLD: 01 Ranger Edge 4 Door 4.0 Lifted on 33's
SOLD: 86 Ranger XL 2.0 4 cyl.