What the perforation is for
Air moves through it. That matters for produce that respires or sheds field heat, for anything washed and left to drain, and anywhere a load would sweat inside a closed box.
It also costs you nothing structurally. Every rating is identical to the closed box, including racking, and the perforation makes it 2.20 lb lighter.
The trade is obvious and worth stating: fines, powders and small loose parts will escape through the slots. If that is your load, take the closed RC-121 instead.









