Be sure to get a drum that is either 1 piece or at least has the bottom (tig) welded on. It doesn't take long for a bottom that is rolled on to leak. Repeated firings will expand/contract the metal well past its intended design. I have a friend who brews with rolled drums and they all leak. He continues to use one as a fermentor and after a few weeks his garage is a mess.
You probably want something like this, there are a number of folks who sell these, here is the first one that popped on google for me: