The second attempt at a tube used a single layer of cash register tape lengthwise instead of spiral wrapped, and a spiral of packaging tape. The tube was made the entire length of the mandrel (20cm). Instead of the Adtech epoxy I tried using APC EZLam epoxy since it is easier to mix in small volumes.
The tube turned out slightly large still, however it is possible that it is usable to build an actual rocket out of it. The tube can probably be thickened with a single layer of paper epoxied into the interior, or the motor can have tape added to improve the friction fit. It also seems that the tube is much softer than the other tubes. It is unclear if this is due to the tube being stretch more, or the different epoxy, or the epoxy not curing fully due to the recent drop in temperature. Even though it is softer, it is still stiffer than a cardboard tube, and adequate for the forces it will see in flight.
My next thought is to try making a part using a 6mm rod with the normal paper and tape wrap. That technique was by far the easiest to remove. The single layer lengthwise wrap was difficult, and resulted in destruction of the dowel, whereas the other part was relatively easy to slide out.