JD's Garage Micro
After pre-drilling the holes for the wood screws, I used a table with a built in clamp to clamp each side piece upright, and screw in the screws until they just barely stuck out the inside surface where they would meet the 2x4s.
Here's another shot from the inside surface of a side piece. If you look closely (you may need to launch the full size image using the link below) you'll see that the wood screws are sticking out ever so slightly on the inside surface. This helps when positioning 2x4's before screwing them in because each wood screw tip functions somewhat like a small tack holding the 2x4 temporarily in place before screwing the wood screws all the way in.