Surface mounting box on ribbed metal panel with wire inside wall?

[larrygerald]

How can you do this neatly and still have the required strain relief? We plan on putting having the wires concealed in panels then the boxes on the outside for simplicity. Box won't sit flush with the strain relief on the back

 

[readhead]

Put a block where you want the box. Drill a hole big enough for the connector. The box will cover the hole.