Got back from visiting relatives today. Finished setting up the top of the rim where I wanted tonight, so I glued the top to the rim.
I spent a lot of time getting the top so that it fit nicely to the sides, without much pressure necessary to hold it in place. Still, I used a few clamps in critical areas just to make sure everything is tight.
I used a bicycle inner tube. It's a single inner tube, that I cut with a scissors in a long spiral, to make it about four times as long as it started out.