One of my main problems in buying tackle boxes is i usually end up with having dead space that i dont really use. The way i fish i dont need to take extra tackle boxes and the ones i take need to have every square inch of space accounted for.

Ive been using the Rubber-Made file folder boxes for tackle boxes. The particular ones i use will hold either 12 Plano 3705 or 6 of the 3700 utility boxes. They fit perfectly with no slop between box placement.
There is also plenty of spots to attach a nylon shoulder strap and if you put a couple of product advertisement stickers on the sides it looks like an "official products" tackle box. I actually had a couple of guys come over and ask me where i got the Gamakatsu tackle boxes.