Fedex (every location) gives away a free adhesive backed clear label holders intended for you to stuff the shipping label into and then apply to one of their boxes, turns out this free label holder is about perfect for this mission of a place to put the declaration, and then stick it on your container....that is what I use, it is a great idea offered by nalesq. I too have experienced the failure of the factory ammo box, I got a small nylon mesh bag that holds two boxes and even if they break open the bag will catch loose rounds.
Delta has been doing this queer shit with the huge plastic tie wraps and requiring you to pick it up at their oversize baggage claim. So take a set of nail clippers or a TSA legal set of scissors to remove that crap after you have your bag and have exited their baggage office.