Bottom is still needed. The refractory box I got last year was the same as my 19 year old one, so I'm not sure to what Burner is referring. It sits down in front, and the inner rear plate benches up against it. It'll make sense when you get the inner plate installed. BTW... list price on that chamber was only $250 last year. Might want to get another price on that, before dumping $419.