I have made fireboxes made from 1/4" and 3/8" steel but I always wanted to build one out of 1/2".

Found another Craigslist ad posted by Terrel and he was offering 1/2" plate at the right price.
Just about 100 miles away or so.
So I went and snagged two pieces of 1/2" x 8' x 10'.

This was enough to build three fire boxes!

Loaded it up and off I went.