Not seen a video as Bob said also you can put a rebate in your bottom row of segments and fit disk unglued when you are gluing up your ring. Dennis Keely has it detailed. It is shown on Segmented Woodturners Forum look under projects.
Bob, this bottom is actually a combination domed bottom and floating bottom. I think if I was going to do a true floating bottom like Malcolm shows I would make up the same type but a thicker disc. I would then cut slices maybe 3/16 and glue them together 90 degrees apart between a 1/4 inch plywood. That would take out any movement issues. I hope that makes sense.