[bllfish]

I would cut a large square in that corner. Believe me, I just went thru it. Eventually the seal goes or you move something and the "DRIPS" start running down you drain line. Trying to tighten or replace the bulkhead fitting is almost impossible without a LARGE hole. Your tank is only supported around the edges. The bottom glass touches nothing so you can remove as much as you want as long as the edges are intact. You actually do not need the piece of wood you will be cutting for the drain/return line. If you look at a lot of stands, there are one or two braces spanning the width of the stand.
Great looking stand by the way. I wish I had done it your way.
One more thing, I would caulk all the inside seams and then paint with an epoxy paint to try and water proof the stand. This would also help to contain the inevitable spill or overflow.