I use and have always only used a 16" round terra cotta tray as a diffuser. I have no problem with dry BBQ and no trouble with temp control.
Now, how much and the way my fuel is started can cause some temp problems but they are usually always brought back into control by just adjusting the input vent.
I don't buy the whole water pan theory, myself. But, I've never struggled with temps in my UDS so what do I know?
Good luck, bro. Just keep trying things until you find what works for you. That's going to be the best way too cook BBQ.
Jambo Pit - UDS - Lang 60 (Sold)
18.5" & 22.5" Weber Kettles - Smokey Joe and Mini-WSM - Bubba Keg - #2 La Caja China
Impeccably Accurate BLACK & RED Thermapens
Operation BBQ Relief Founding Member
I am Obsessive Compulsive about BBQ. Google it.