Why? Can't you fit a double DIN unit into the RRS like you can with the Discovery 3 and 4? If so, you should really reconsider your choice of the Halo 9 and look at the Alpine iLX-107 <
iLX-107 - Alpine Electronics of Australia > instead. Many reasons - first I cannot see anything the Halo 9 does that the iLX-107 doesn't do, secondly the iLX-107 has a big advantage over the Halo9 in that it is Wireless Apple CarPlay (not USB cable only like the Halo9), if your an iPhone user then that should be enough to sell it to you, thirdly, it's $500.00 lower listed price should mean you can obtain it at a much lower price.
The only exception to the above is if you are an Android user as I think it doesn't have the Android Car features at all.
Part of me really wishes I had just spent the time to make up a custom double DIN centre dash surround for my D2...