I've completed a custom install of a VDO boost gauge in my 2003 Audi RS-6. There are no pre-fabricated pods for the RS-6 so I had to fabricate and customize one of the dash vents to hold the gauge. The install was time consuming, but it came out well and gives me a real time view of boost levels.
I tapped the boost line into the vacuum hose between the fuel pressure regulator and the intake. I had to get a bit creative on how to route the hoses to keep them from kinking. I also replaced all of the other vacuum lines since most looked pretty old and had visible cracks.
Vacuum Hoses and Boost Line
To install the VDO boost gauge in the vent, it took quite a bit of fabrication to use the factory directional vent vanes. They looked pretty rough during the fabrication, but it turned out fine.