Measure and cut two 24-inch pieces for the top and bottom and two 18-inch pieces for the sides from the 3/4-inch 12-inch wide board. Because the board is actually only 11 1/4 inches wide, that is how wide each of the pieces will be.
Assemble the pieces into a rectangle by placing the bottom and top pieces on their narrow ends on a flat surface, parallel to each other leaving enough space to slip the two side pieces in between.
Apply wood glue to the short ends of the two side pieces and then place them between the top and bottom pieces creating a rectangle. Place the strap clamp around the rectangle and allow the wood glue to dry overnight before removing it.
Measure and cut a 19 1/4-by-23 1/2-inch piece of hardboard. Center and attach the hardboard to the back of the storage bench using 1/2-inch finishing nails every 6 inches. The hardboard will be slightly smaller than the outer edge of the storage bench and you will place the hardboard so it overlaps the wood all the way around the back of the storage bench.
Turn the storage bench upside down and install the leg mounting plates on each corner of the storage bench by inserting a screw through each of the holes around the outside of the plate. Offset each plate from both edges by 1/4 inch. Screw the flat end of the hanger bolt into the central hole of the leg mounting plate, insert the pointed end into the predrilled hole in the top of the leg and screw the leg on.
Cut two 24-inch pieces of the trim you selected to fit the top and bottom edge on the front of the storage bench. Coat the front top edge of the storage bench with wood glue. Position the decorative trim so that the flat edge is aligned with the top edge of the bench, press it into the glue and nail it in place using the finishing nails. Repeat for the bottom trim.
Sand any exposed rough edges of the small storage bench, first with 100-grit sandpaper, and then with 400-grit sandpaper.
Prime and paint the small storage bench to compliment your decor after removing the strap clamp.