At Mason Dixon Bowhunta. You only need the ball valve on one intake. The first uds I built I used four 1/2 pipe nipples and I used a regular gate valve that is used on waterhose applications and to be I can keep it around 240 degrees just by using the caps on or off with the valve completely open. The next drum I built I got the drum from a friend with the holes drilled for 1/2 nipples but he messed up the hole spacing so there was a larger gap between one set of holes. I drilled a 1 inch hole in the middle of that space that space and installed a 3/4 nipple with a ball valve. That drum sometimes I leave one nipple off and regulate the airflow with the valve and sometimes I just use the valve with all the nipples capped depending on weather conditions. I believe that if a guy was on a low budget he could put in six equally spaced 1/2 nipples and regulate the temps just using the caps on or off a few nipples.
Backwoods Fatboy, 2 Ugly Drums, 22.5 wsm and 2 18.5 wsm's.