+ 1 on cooking fat cap down on the UDS, and then fat cap up when wrapped in foil or butcher paper with no additives. The fat cap down helps insulate from the direct heat of the UDS. There is enough (or should be) fat in the brisket to keep the meat from drying out so fat cap up is not necessary to retain moisture. There is plenty of natural moisture present when cooking with a UDS as long as you keep the lid on and don't peek while cooking. Peeking lets the moisture out and causes the temp to fluctuate wildly.
UDS, cheap o grill, rusted chimney, yeller wannabe thermo pen, Maverick ET 732, 1950 model wife.