Man so much empty space in boxes devoted to extensions... I used to use a small shallow drawer in my bottom cabinet (a 26", the top 4 drawers are half width)for my ratchets and extensions, just loose in the drawer. copied my ol man for the long ones (18, 24, 36, +) by drilling through the top of the rolling cabinet at the edge so the extension is hanging in the wall of the tool box.
I also keep a couple of 1/4 socket sets in their clam shells (Older Allen is a tin box) and added a 4 and 6 to each case for out side repairs when I need a set away from the box. I plan on keeping a 6 in the Hansen tray right between the rows when the tray arrives since in my line of work (power equipment) that's the most used socket set and length extension.