They have these old black oil changing barrels, about 35 gallon tanks. Y'all think they could work as a UDS?
I could be way off here, as I have not been keeping up with all the improvements to the UDS builds....but I would think with that small of a container, you will be looking at having to add a water pan to it. Ask around
Like dirtsaylor said, no water pan needed. A simple diffuser works fine on low cooks and many times that isn't needed either.
I tend to go to my smaller cookers more than the 55 gallon cooker. You can cook a bunch in the small ones. This cooker is smaller than your oil drums and you're looking at 44 lbs of pork butts in it....5 1/2 hour cook.
Plus those oil cans look like they are thicker steel as long as you run water and a good degreaser through it before cutting it open you should be good to go. the rest you can just burn off alot of people on here like to get pallets cut them up and burn out the drum really well before putting any hardware in it. but if you do this be sure to drill the necessary holes before you burn to insure more O2 flow