It might work, it will take a fare amount of skill to weld up the thin stuff and look nice. Then possibly line it with fire brick. I have never tried it but the old man across the street says you can stack the brick in a manor like an arch way cutting the last brick to fit tight. He says he did it to his own SFB rig years ago and it was not until he left it sit for years untouched that it rusted out.
Probably work. Probably alot of work. Probably pretty heavy to.
My self I might try 3/16 if my rack was elevated and I was building it with an air space outside for temperature retension.
I was just thinking I would probably need to cut the box in half, or maybe in thirds, couldn't I just double stack the metal? And I know alot of those jobboxes aren't that thin, especially the diamond plated ones. Just to be clear, I am talking about those big tool boxes that you mount accross the bed of a pick up truck.
I know there is a post around here, from a LONG while back about the gauge of metal. I have to agree with the others when they mention the gauge and material type. Research that & you may find your answer.
most diamond plate truck toolboxes are aluminum so they wont be able to be welded to steel. i don't know if aluminum will stand up to the heat of a firebox, since i've never seen an aluminum smoker, however i'm not saying it can't be done. some of the black diamond plate toolboxes are aluminum with poder coat on them and that powder coat stuff is hard to get off.