Plan on using a drip pan, or putting the bird into a pan.
I spatchcocked and cooked a 22 pound turkey on my UDS. Turned out great. All I did was dry rub it, and put it on. About halfway through the cook, I had to put it in a pan. The juices were dripping onto the coals, and putting them out. Plus, turkey fat stinks.
22.5 OTS(H), 22.5 OTG(DA), 22.5 Daisy Wheel Kettle(EE), NBBD, UDS, MUDS, 6-burner gasser