Hi Shortbus,
You have the right idea, the only thing is that the tubes are not perfectly round when we receive them, so piece of round stock would not be able to properly seal without putting a decent step feature at the end of the tube. Secondly, the surface roughness must be 32 RMS max, which can be easily obtained by any turning. As you have mentioned, lathes are a dime a dozen here, only thing is that the tube length is too long for standard lathes. To fit a ~60" length tube into a lathe, you must have a tail stock which would add an additional 2-3 feet to the bed. I don't know, I feel like I am spinning. We have a line on two individuals who say they can do it but we have been down this road before. People say they can do it and then when we show them the work that it is actually almost 60" long they renig. Do you know anyone in Ohio who can do this? I know they have a lot of metal work out there. It is actually being rolled from sheet and welded up in Toledo.