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1. You should be able to round the barrel again, or at least get it close enough, by rolling it on its side on flat concrete while rolling another smaller wheel inside of it. Bring a rubber mallet for those really out of whack spots. I know that sometimes when they really get hammered crooked, it's difficult and tedious to get it close enough to work.. if not impossible.
2. You can fit a standard "Weber Kettle dome lid" on the top and get it to seal with relatively little work. All you'll need to do is rubber mallet the edge of the lid to get it flat(ish), and then use the metal ring that came with the barrel and lid to re-form the lid's edge to the edge of the barrel. Just walk around it banging at regular intervals until it seats. You'll want to line it all up correctly before doing this so you'll have a reference later for where you "custom fit" you new lid.. which, by the way, will add capacity. Meet your new BIG turkey smoker.
P.S. Galvanized anything is a bad idea. Although there is some controversy over whether or not a smoker gets hot enough to actually pose a risk, Zinc poisoning = BAD.
Here are some ideas for lids and making the UDS taller also....... once you get the drum straight and the lid clamped on..... or if you have a non-lid drum......