Any idea of the thickness of the tank walls?
They are thin. The rings shake like jello when they are being moved around.
Musk explained Friday, in response to a question about whether SpaceX would use water tower machines to make its rockets, that unmodified machines don’t work great due to lack of efficiency. The Starhopper, he explained, used 12.5 millimeter thick steel. The SN1 prototype uses four millimeter thick steel. For optimized versions, they could go as low as two millimeters in areas with a circular steel design that measures 9,000 millimeters in diameter.
https://www.inverse.com/innovation/spacex-starship-elon-musk-explains-how-it-will-beat-a-water-tower