Building a padded storage bench only takes a few tools and materials. Make sure you have fabric shears and a staple gun along with batting, fabric, muslin, open-cell foam, spray adhesive and staples.
Secure the foam to the plywood
Trim the foam with the fabric scissors to fit the area you want to pad. Use shears to cut a 45-degree beveled edge on the foam. Apply the spray adhesive on one side of the foam and on one side of the plywood backing board. Center the foam on the board then let the adhesive cure.
Add the batting
Stretch a layer of batting around the foam and backing board, smoothing it out in the process. Lift the batting, and apply the spray adhesive to the underside of the batting and the top of the foam. Smooth it out to let the adhesive cure properly.
Add the muslin
Stretch the muslin over the backing board, foam and batting, leaving enough extra around the edges to wrap the muslin all the way around the board. Staple the center of the long edge, then staple the opposite side in the center putting enough counter pressure to keep a firm fit. Next staple the centers of the short edges the same way. Staple the batting and muslin all the way around the perimeter of the back side, trimming off excess muslin in the process. Lightly tap in protruding staples with a hammer.
Add the fabric
Wrap the fabric over the muslin by stapling it to the back of the board the same way as the muslin.
Add the cushion
Add the upholstered cushion to the storage bench, and nail the front trim into place