first, for weight savings, solid walls can have sections cut or scalloped out. the top panel, for example, could have a pattern machined into it.
second, to decrease overall dimensions, remove sections from the side. for example, instead of having solid edging all the way around, have the top panel only extend to the edge in the few places that it needs to be fastened (via screws) to the bottom panel, or barring that, cut some kind of honeycomb into the edging.
unfortunately, it doesn't sound like many other folks would be into this, but i'd be!