I don't know about the liners, but I do know a trick to burning those things clean. Stick a chimney in there on top of your fire. A 6' or longer section of 8" stove flue is perfect, but hopefully you have some scrap laying around like that, 'cause it's gonna get toasted. It does an incredible job. Your fire will burn so hot that the outside of the barrel will be completely clean of all paint, let alone the inside.
Cooking on a crazy contraption...