Heinz,
That was the route I went. To install the aerial, take out the drivers side speaker and drill a pilot hole from the inside. This means you get the location right. Then enlarge it from the outside just enough to get the wire through. Having installed the aerial, put some silicone to seal the wire hole.
I used a Sony radio so I could use their wired remote (part X4S) and mounted this at the rear of the transmission tunnel. I can do anything withe radio without looking at it at all! Very safe - no fiddling about with a small remote trying to press the right tiny button!!
Cheers!