I would suggest using cardboard toilet paper rolls or paper towel rolls.
Start out with the original diameter and use a small ring cut out to fit around the external edge of the front, and internal edge on the back, use another roll and cut down the side so it will fit inside the other; do the same thing with the ends as the prior. Repeat this 3 or 4 times. You should end up with something like this: (graphic coming soon)