Stand your three cabinets in a row, with the doors all facing the same way. Apply wood glue to the sides of the middle cabinet, then press the other two firmly onto the sides to join the three cabinets together.
Paint two planks of 36-inch 2-by-12 lumber in the same color as the cabinets and allow them to dry.
Lay one of the painted planks flat on your work surface and place the three cabinets on top. The lumber should be flush all around with the bottom of the cabinets.
Secure the cabinets to the lumber plank with a 1 1/2-inch screw through each corner of the cabinet base into the lumber plank.
Place the remaining lumber plank on top of the three cabinets and secure it in place like you did the base plank, with screws through the corners of the top of the cabinets.
Place the cabinet bench in the foyer. Sit a 12-by-36-inch box cushion on top to finish the storage bench.