I got bold and cut the top rim from my drum, partially because the flat lid I found would nit fit INSIDE it, and probably a Weber or other dome lid would not fit OUTSIDE it. And fired off another test burn. Wanted to have more solid experience before I throw $30 worth of brisket on it :-). I placed this pampered chef stone on the lower rack and checked the temp 5" above it, and right below it.
Running with just the 3/4 ball valve open and around 8lbs of RO lump in the basket.
375f below, 250f above it.
I did check both my short and long thermo's the other day in boiling water and they are right on the money around 212.
That stone I made the mistake of "seasoning" it with canola oil, basically ruined it unless I can find a person with a pottery kiln to refire it, we do not have a self cleaning over either, people have reported cleaning them in one.