Do you have a 5C collet system for your lathe ? If so, I would use a step collet to support the part at the head stock. I have used them for thin walled pieces and they work very well and cause no distortion of the part. You purchase them in "blank form" and machine a pocket that exactly fits the OD of your part to be turned. Then dial in the other end in your steady rest. The link below shows an example of a step collet.
Ted
http://www.ajaxtoolsupply.com/5cstc...5cstclco3hed&gclid=CNbN89j__84CFQqPfgodLqQHrg
Just thought of another option. Machine a set of pie jaws for your 3-jaw chuck to fit the tubing. These also will chuck the part without distortion.