Is there something like a jubilee clip (hose clamp) that is extra long?
You can open hose clamps completely and chain them together. They're readily available in 6" diameters and perhaps larger. 

You could also purchase a ratchet strap for about the same cost. It would let you avoid having screw buckles showing at intervals. 

Or you can use about any chain or strap you like along with a turnbuckle.