Phong - I added a vertical center brace in the back via a half lap joint. Each half lap was cut on opposite sides of the boards in an attempt to the center brace from twisting. The front also has a center brace as well, but it is attached via pocket screws on the skinny side of the 2x4 this way it can be removed when and if I need to do major work on the sump.
I'll take some pictures tonight.
I'll take some pictures tonight.