I finished up the last bits to get the rough drain line in. Glued in a 9 foot section of 1.5" PVC pipe. It runs to the right side of the rear wall as that's where the two sinks will intersect with a single common drain. Note the open floor at the far right side. This is to make sure if there are any drain leaks the water goes right down to the vinyl floor. You do not want a storage shelf under your drain!
I used a hanging strap at the right end to raise up the drain. Plenty of flexibility in the PVC pipe to do this. I glued a scrap of 2x2 wood to snug up the strap fit:
Three pieces of scrap 2x2 cobbled together for a center support.
Now to install the 2nd shelf and the rest of the sink support frame.