Im building a 500 gal. reverse flow smoker, my tank is 48 in. diameter and 60 in. long, Feldons says I need a 36,172 in. cu. in. firebox.. this comes out to roughly a 32x36 in. box, well Ive got the box welded up and this this is giant, its made from 1/4 in. plate and probably weighs 300# or...