Just checked it out. Requires a 3/4" hole in the roof 10-12" in front of the third brake light. The antennna is about 3" wide and 5 " long, 2. 5" tall. A bit too large to be able to fit under the dash plastic. The way it works is that it has a 3/4" "fixed connector" with two wings which snap into the hole. A gasket on the base is compressed when the wings snap in an keeps the water out. Looks like not much choice for a different kind of mount on the cab, unless you fab something to stand above it. If you have a cap, you probably could move it back there, but the snaps are designed for the thickness of sheet metal.
There are other antennas out there for after-market. This is an Alpine rig... . wish I could give you better news.....
You use one harness if you dont have a CD changer, another with a switch-box if you do, controlled by the radio head, of course.
Let us know how you like it... I haven't decided yet about adding it to mine... .