I’m not doing all of the faces, the top and bottom will remain open, very probably the front, though that remains to be determined. I may just do the lower part on the front below the cross bar.
It’s not a new idea, the Railcore was designed this way, using 1515 extrusion and a skin surface to make the structure more rigid. I don’t remember what material the Railcore was originally specced with, but the idea was the same, like a torsion box, using the skin to reinforce the structure and keep it from deforming.
With just the back plate though the whole frame feels more solid, and the back is like a granite slab. This is with 5.5mm plywood, but I’m pretty sure it would be amazing in 1/8" acrylic, as well.