Sweet looking little tank Colin!
You could check out Reef.org's old Nano Reef Buildoff thread for some ideas, I know there were tons of DIY creations.
In the Red Sea Max they only have a small section ~4 inches notched for the overflow, and then a little plate that can slide up or down to make better surface skimming. If the plate is up too high it becomes a little noisy, but once the surface is clean you can slide the plate back down.
It could be an idea.
-Diana