Thanks - took longer than expected, but here's some more pics of the rig for your viewing pleasure. There's just mesh on the inside - didn't want to get too complicated.
You can adjust the shoulder straps, they secured with velcro. Here's a picture of the cummerbund with elastic and 550 cord so you can fit it snug (adjusts longer or smaller, though it's near it's smallest point in order to through the back panel):
Cummerbund slides through here:
Here's the side flap where the end of the cummerbund attaches to:
Lay it on:
and close the flap down:
and then repeat for the other side. The easiest way to do it is to leave one side attached so only one side needs to be secured, which can be done in just a couple of seconds. I may go with some padded shoulder straps depending on how it feels all loaded up. Also the shoulder straps are 2" wide with 1.5" webbing for extra durability: