Assemble the Bench
Assemble the box frame by first attaching the front panel to the bottom. Use wood glue and finish nails to hold the unit together during assembly. Add the back panel next and then the two side panels (Image 1).
Once everything is assembled and fits together properly, reinforce the structure by screwing all the pieces together with 1-1/2” wood screws (Image 2). If you plan on covering the banquette with beadboard, do not worry about the screw heads being visible. If you decide to paint or stain the bench, you will want to counter-sink the screws enough that you can cover over the heads with wood filler.
Add braces at each corner for extra support and to hold up the top frame. Cut scrap pieces of 3/4" plywood at two 45-degree angles to create a triangle. Make sure it fits snuggly into the corner flush to the top of the vertical pieces. Attach with wood glue and screws.