That is one cool clamp rack. I might steal the idea, but given the discussion on joinery and hinges probably modify it. My thoughts to improve it are attaching both outer boxes to the back unit by having the middle box swing left and the front box swing right. In order to do that one would have use a wider board (at least on the lower area) on the right side, and make the middle box a little narrower so it would swing past that side.
The other change i would make is to the middle box. The top shelf is supported with angle blocks, where the bottom shelf lacks the same strength. That could be provided by moving the bottom shelf up and cutting a dado on 3 sides or lengthening the sides and the bottom back piece allowing room for the same supporting wedge blocks on bottom much like the top shelf.