I've done door enclosures in other cars, not in my p-car though. I'm not really concerned with the radio in the porsche, the car makes it's own music
If one were so inclined the passenger side kick panel make a good spot for a custom 6.5" or 8" enclosure. I've also seen custom center consoles that utilize the forward compartment space to mount up to a 10" sub that fires sideways.