Just because they have a red liner is not a reason to pass on a barrel. A couple of burn outs and you are good to go. In all reality and common sense, once it has had two good burn outs, any remaining liner is a moot point. If two hot fires that burn the outside paint off leave any liner on the inside, then the danger is gone. Once seasoned, the barrel will not get hot enough to burn the outside paint off from cooking on it, so it will not get hot enough to cause the left over liner to put off harmful fumes. The air you breathe on a normal day has more toxins in it than you would ever get out of a burned out barrel with a small amount of red liner left in it. You will get more toxins from a cheap smoker from Home Depot that is painted on the inside of the fire box than from your burned out barrel will ever emit.
I will now step down from my soap box and go fire up my UDS to cook some yardbird on that had about 1/8 of the red liner left after two burns on that I made over 2 years ago. 70 years old and still going.
Blessings,
Omar