I'm not sure if you have got this figured out yet or not. While I am far from being an expert, I would add a narrow first chamber as a raw water chamber with your overflow pipe extending below the water line. I then have the water running over the baffle into filter socks. I have only three sections - 1) raw water; 2) filterocks/skimmer; 3) GFO/Carbon reactor and return pump.
I wish that I had a refugium and have been looking at ways I can modify my sump to add one.
Here is a picture of mine
