I have an idea... What if I go to Home Depot and buy a 3/4" sheet of soft foam (not glass fiber, something more pleasant to handle) and a piece of piping or plastic tubing that's 1.5" wider inside in diameter than the 1500 tube's orange flanges. Maybe little less for a tight fit. Then cut the foam and pad the inside of the tube, perhaps glue it in place. Tight, but free of buckles. I should be able to stick any 1500 tube configuration with two or more joints in there, nice and snug. The isolation might even help maintain the developer temperature as measured before it goes in the tank. I say it's worth a try! If it fails or is problematic in practice I can always pick up used tanks later...