Start by cutting dowels to fit the length of your 2’x4′ plywood.
If you want a cleaner finish I recommend cutting the ends at a 45-degree cut on all the corners where your dowels meet with a miter saw.
Be sure to measure twice before making those cuts. Now it’s time to assemble your frame!
Apply wood glue to the bottom of each dowel and attach them to the plywood.
Once all of the dowels are in place, use a brad nailer to secure them.
Before you start using brad nails be sure you have the proper length so your nails don’t poke through the back.