A lot of us over the Tasmain are usin the Hella 5242 Universal External Mount High Level Brake Lamp. This is a die cast metal housing designed to bolt to your boot lid or on the rear deck in the center behind the seats. It's a neat low profile design and doesn't look to obtrusive when painted to match the car.
Here's a link to the details on it:
Hella 5242 stop light
Here's a link to the Hella web page in NZ:
Hella New Zealand
Cheers