Sounds like a lot of work to me.. Why not use some 1/2 inch pvc or
wire hoops, and just bury the edges in a few inches of soil at the
edge of your box? The material is secured by running cord over the
hoops. If you have high winds, roll the sides 2-3 times over a 2x4.
Generally you'll want the material to cover your crops but not be too
restrictive, so the height will depend on what you are growing. Maybe
12-18 inches for lettuce, much taller for broccoli.