NM Clamps in Boxes on Exterior Walls
The main thinking of inspectors in my state is making sure that that NM cable entering any metal enclosure is properly bushed to prevent the bare metal from cutting into the conductor insulation. Manufacturers make plastic bushing just for this purpose. It snaps into a code size hole and has "Fingers which hold the cable in place. For reference try Googling "plastic romex connectors" and see what pops up. I know Arlington makes these thing as well many other manufacturers.