I don't have the pics right now, but I initially used Randy's mounting brackets and that worked well.
Since I have to fly it in snow, I ended up putting Pixhawk and other components in a waterproof case and hanged it below the frame (directly under the main shaft) using a floating mount. I also use tall skids take from 500 size helis to gain more clearance from the ground.
Regardless of how you end up mounting it, you really need a good vibration isolation/dampening mechanism.
EDIT: Here's a picture of the configuration that uses Randy's mounting brackets. Please note that this was after I converted it to FBL (you can see the Futaba FBL controller mounted on the side of the frame). Also, the floating mount pictured here was inadequate in isolating vibration, but I don't have the pics for the improved version...