First, my lathe is a Nova 2000 with a 16" swing so I have to work within that restriction. It does have a swivel head but ...

Originally I was going to make the cylinder 18" deep but thought 13" might be less of a problem.

I've got cole jaws with extensions and can make a plate to press against the tailstock side to turn the outside smooth. I suppose I might be able to make a ring and attach it with long threaded rods to the cole extensions - similar to a donut. Is there another way that would fix/hold the tailstock end of the cylinder that I could buy or build that would allow me to turn the inside to a consistant thickness? I know it's a long way off the toolrest but I could do one end (say top) and then reverse it and do the other (bottom). That way I'd only be working a few inches off the toolrest - I have a toolrest that can extend partway into the cylinder.