They fit in almost perfectly and the boxes stack well, allowing for space-efficient storage. I just went and bought a bunch more for the whole collection. Another layer of 11 tapes can be shoehorned in if easy access isn't an issue. A little pricey, but quality construction. I live in Boston, and went to one of the local wood shops that builds unfinished stuff.
Tapes have a little bit of room allowing for easy removal.
Thing does not look the nicest as it is black plastic frame with clear drawers. Each drawer holds three rows of 23 DATs, with just enough spare room so you can pull out any tape easily. It has wheels for easy moving too. I belive these are smoky-clear plastic drawers in a plastic case. Looks like it was made by Tupperware or Rubbermaid.