I tapped my boost gauge in the cast tube on the passenger side of the motor that runs from the intercooler to the top of the motor next to the alternator. I installed it on the back side of the pipe so you couldnt tell it was there unless you removed the tube. It also seemed to be the easiest part the take of and drill and tap.
The easiest and most common sense place to put it is in the tin tube on the driver side or a rubber duct tube. But Id be affraid of it blowing out leaving a hole or leak.