I wasn't sure how I was going to mount the sink. Usually, there's a 3/4" hard-deck of ply under the stone that you can secure mounting hardware to, but in this case, the stone was dropped right on the framing. I ended up doing some Google-fu and found a simple product called a Hercules Universal Sink Harness for $5. It's simply a "sling" that secures to the cabinet structure and a turnbuckle style gizmo to snug it all up.

I put two of the mounts on the door opening with long screws through the Trex backer and into the steel frame... You can see them near my Sharpie marks on the Trex piece.