I'm building a cube tank similar to bananatropics 30x30x24H and I'm having problems figuring out how to work an internal overflow, so I'm now thinking outside the box.

I want to do a short overflow along the length of the back (20x5x5) and just drill a row or two 1/2 holes in the back wall (holes stronger and easier than slits). Would this weaken my tank too much? Are there unforseen problems with extenal overflows?(Tank built out of 1/2in acrylic) Thanks - Tim