Next, with a friend, flip the plywood and batting over so that it's resting on top of a larger sheet of batting. Trim the larger batting so it's 6" wider and longer than the plywood panel. Pull the layers of batting tight and secure the larger sheet of batting to the plywood panel using a staple gun loaded with 1/4" staples. Repeat this process so all three plywood panels are wrapped tightly.
Place the three panels face down on a clean surface and butt them up tightly to one another. Place a 1x3 on either side (about 15 inches from the edge) to connect the three panels together. Secure in place using 1-1/4" wood screws. Note: The screw's size is important, so it doesn't pop through the other side of the plywood.