Hi denso,
I recently fitted a GME 3550S to my Landcruiser 200 series I fabricated a bracket from aluminium using factory bolts
Under the dash on the drivers side. The mic I mounted on the dash drilling 2 knockouts to avoid drilling the the dash.The knockouts are cheap and easy to replace if you want to remove the unf.
The fabrication didn't take too the designing took the time.
Cheers Dibbo.