Out here we'd call that a smoker, not a BBQ. Our big grill is brick, with a grill made of crusher screen from a nearby mine. It's about 30 years old now. Too big to use unless you're cooking for a wedding .Old and lazy now I bought a pellet smoker for everyday use.
Welding up your rig would no doubt be faster, but bricks don't rust. Source for fire-bricks? They can be hard to come by in small quantities.

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