Gary,
The case dimensions on my cabinet are 18-1/2" wide, 30-1/4" high, and about 48" deep. I think this was the biggest case I could get out of one sheet of 1/2" ply. It does let you store and fully protect any 48" balsa you have. The top has birch edge molding on it, so that is wider than the case. The bottom has base molding, so it is about 1-1/2" wider than the case. I left the back open, as it seemed sturdy enough against the possibility of racking. The plywood edges of the front and back are finished with birch edge banding. I used a preglued version that you iron down. That worked fine and has held up well so far. The shelves are also 1/2" birch plywood; the partitions are something like 5mm luan plywood. The thing is dadoed together. Probably biscuits or a tenon on the top molding. I think the finish is Danish oil. I left the interior unfinished as I didn't want it contaminating the balsa.
One of the things that did come over from prior storage methods to this is the use of cardboard tubes to segregate and organize certain strip stock and similar. You can put all your balsa square stock in one. All your basswood strips in another. Piano wire, pushrods, carbon tubes in another. Separate it out until you run out of room. If you can't see your piece, pull out the tube and dump everything. Find it, then slide the preloaded tube back in.
It does ok with blocks but is not as space efficient. Most blocks are not 48" long. If you insist on shoving all the blocks you have into it, you have no idea what you have hidden in back, and they are hard to fish out. When things get pretty full, it is easier to put a sheet of paper underneath the sheet wood and leave a tab sticking out that you can pull out the whole stack. That also works between groups of sheets. For example, between a bunch of 3/32" sheets and 1/16" sheets. Pull the tab and all the wood on top--say all the 1/16"--slides right out.
I like putting all the thicker stuff on the bottom and thinner as I go up, then often put some good 12-14 lb "racing wood" on the very top of the stack to keep everything flat. The other thing I do is put the half-used sheets right at the top. In that case, no heavy full sheets on top as flatteners. Where this pays off is in 1/32" sheets which tend to wrinkle and twist with little encouragement. One-sixteenth does too, but not as bad.
Now if I could just get any other part of the modeling stash under control, like an out of the way rack for the MonoKote leftovers....
Dave