be modified to work with a Pioneer navigation unit?

the trunk is made out of composite materials (nice way of saying plastic) the GPS antenna goes on the inside of the trunk lid...
you can glue an aftermarket antenna to the inside of the trunk and it will work - has been done before on the cab.
hope this helps

Somebody fell on the back og my car about a month ago driving an old honda and he made a hole (!) on my trunk and some minor damage on my bumper. The trunk certainly wasn't made of metal. It looked like the material my boat is made of. Of course my trunk was replaced.

The trunk is composite. The piece just in front that rotates to accept the folded top is metal. Add a few inches of slack to the antenna wire and your good to go.

I have a mag mount antenna for a EMA radio and thats the only ground plane the CAB has.