I have this Hoffman 16x14 stainless box, to control my rig which is in high build phase. I intended to put 2 30 amp twistlock outlets on it, which involved attempting to drill 2&1/8" holes with a bi-metal holesaw on a drill press. DON'T TRY THIS! The stainless on these is SO incredibly strong that it just ate the bit and made a big ugly spot.
So here is my solution:
30 amp dongles! All I had to do was drill 7/8" holes in the bottom with a step bit and install these cord grips with the rubber sealing gaskets. Something to consider if you're cutting your own box.