I previously posted a tutorial on making a display box. The method for making this storage box is slightly different from the display box, but the concept is similar.

For the display box, the base plate has holes for the base, and the sides are inserted into each other. For the storage box, the front and back panels have holes for the base, and the left and right panels and the base have insertion points to fit together. Therefore, the front and back panels need to be designed to be a bit longer to leave space for inserting the left and right panels. The length of the left and right panels should match the length of the base plate.