I can’t get up between the joists unless I want to tear down a drywall ceiling. As much as I hate that damned ceiling for the way it prevents access to the area above, even if I did tear it out the joists run in the wrong direction for what I’m doing. I’ll keep the idea of using an inner tube in mind though as I could see it’s advantages for where I have to pass metal duct through an interior wall.
As it is, I have the handiest little bungee cords (maybe 3" long) with a plastic hook on one end that will keep the fan fairly tight to the ceiling. I figure with two of those on either side of the fan and a chunk of jack chain for back up it should be a solid setup.