with, and I found some notes about using SS handrail tubing,  approximately 0.12" in wall thickness.  If one were to build matching  muffler components to attach to those tubes, would 0.12" be  sufficient thickness (presuming 304SS or similar)?  Thicker?  Thinner?

Chris;

You're building an airplane.  Weight matters.  .035 inconel is good.

Al G