That's a very good idea. It'd be much easier to cram some hot glue or silicone into the vents and whatnot. Sheeeeite, I could even get that done and done tonight!
Yeah I know, I was trying to find a way around that ... but I think I'm going to hot glue the vents shut and just cut an overflow into the top of the divider wall.
Ah, I see. Why not glue a piece of acrylic or plastic to the back of the vent (kind of like the bottom vent is), and then cut the slots? It might look a little cleaner.
I scored and snapped a 2"x4" section of acrylic and hot glued it to the vent. Then I used a hacksaw to cut even little slits all along the length of the left section. Then I used a needlenose pliers to snap the teeth out one by one. I actually snapped them all out, opting for a smooth overflow versus a thoothed deal. It skims the surface like a mofo. It was cool, I watched all the scum go within 10 seconds of turning on the filter. When I used the hacksaw (it was a mini one with a fine blade) I put my small fish net under it to catch the shavings and it worked awesome. Only problem is that it's kinda oogly. It was too awkward to glue it to the back so I glued it to the front. It'll look better after I put a flat black strip of plastic over it to make it blend a little better.
WOOT.
Oh and ps that DIY skimmer made of PVC is too wide in diameter to fit in the back section.