Wondering about liner myself. I just installed an insert I bought from a guy. At the last minute he remembered he had a length of pipe. It was 2-4ft sections of single wall ss and a 5ft piece of flex ovaled all riveted together and in good shape. Being on a budget and anxious to get it in, I used it. Plus the ovaled flex just slipped past my damper so I didn't need to cut it out, worked perfect.. Thing is, not sure if it is really the right stuff or the best set up.