To start I cut all the trim pieces from the 2" and 3" pine (based on the sizes in figures 4 & 5). Start with Panel A (figure 4) - place the boards on the box to make sure the fit. Start with the top and make the 2" board flush with the top with 3/4" overhang on both sides. Glue the back of the board and clamp to the box. Screw from the inside of the box with pre-drilled holes and countersink the 3 screws. This will attach the board permanently to the box face and you can now remove the clamps. Repeat for the two side boards and then the bottom board. Remember to put some glue on the ends of the trim board where they but against the previous board. You should have overhangs on each side except the top.
Rotate the box 180 degrees and attach the trim on the other "A" panel repeating the same steps from side 1. Flip the box 90 degrees and attach the panel "B" trim using the same glue and screw method as above (figure 5). Flip one more time 180 degrees and attach the last panel trim for the main box.