Agreed. I'd mimic the original plan as pictured but with a series of triangle braces made of 2x4's. You could clap plywood or OSB to each side of the braces to give them extra strength and stability once you have the 2x4's in place and secured to each other, the baffle, and the concrete.I like your idea but I would not use MDF. I would implement a sort of truss out of 2x4's. MDF is wimpy stuff.