What is the outside diameter of the center post? I'm guessing it is a bit over 2". In this size range 304SS tube is still stepping in 1/8" increments for the most part. Give me the diameter and I will find a source. There are many online metal retailers today so the options are great, even for small quantities.
The heat shrinkable tube idea seems like a excellent way to extend the life of the center post. I looked at Raychem and 3M to see if they have an adhesive lined product but most stop at about 1" dia. If you coated the center post with a good adhesive before shrinking that should keep the water out. The center post on Ethan's machine may need a bit more support then the heat shrink tubing though.
The heat shrinkable tube idea seems like a excellent way to extend the life of the center post. I looked at Raychem and 3M to see if they have an adhesive lined product but most stop at about 1" dia. If you coated the center post with a good adhesive before shrinking that should keep the water out. The center post on Ethan's machine may need a bit more support then the heat shrink tubing though.