If you wanted to check or fit the ZR DAB amplifier to a GTC you could probably just remove the driver side (RHD) parcel shelf side support, the outer cover simply pulls off and the inner cover has two screws holding it on, you need to pull away the boot side panel once the outer cover has been removed to gain access to the two screws.
No need to remove the quarter panel trim or rear seat - if you have the wiring there.
No need to remove the quarter panel trim or rear seat - if you have the wiring there.