My method is not Wayne-approved, but I'm a big fan of "window frame" bracing. It ties all four sides together and, if you are using a table saw, it's easy to get the dimensions right becauses the frames are the same size as the top and bottom. Just cut the braces at the same time and with the same fence settings as the top and bottom. (If you're not going to be using a table saw, then I'd go with Wayne's method.)

The bracing I used for my Pi Studio 2 Towers is illustrated at the attached link.

• Pi 2 Construction Pix