Currently, you can place ammo boxes inside of protector boxes and vice versa infinitely. This leads to infinite inventory space as you can utilize the remaining slots in the boxes when doing this. See the attached and linked photos (they are the same) for a visual of how this works. I have personally seen one of these boxes in game, the people doing this are duplicating ammo and protector boxes in order to carry this out.
http://puu.sh/esAvx/fd15d07957.jpg