I've seen temps up around 350 in my UDS during that heat spike when I load my charcoal basket. I was thinking, approximating I'd be able to maintain a 300 or perhaps higher for an hour or two.
With a 16" stone on the lower cooking grate it would sort of build in the heat diverter. It would certainly have more crisping heat than the top stone in a 2 level UDS.
There are plenty of threads around about people doing cornbread and the like in their warmers, low and slow.
Guess I'll have to drop 20.00 for 2 stones, a couple of cheap frozen pizzas and make a new thread? Give me a couple days LOL
Rich (eatrbbq.com) Weber, Chargriller, assorted UDS