Pls don't give up thinking! Never my head would implode!
If you vulcanize you may be able to attach the edges of the envelope to the flat of the plates and do away with the faces of the envelope. Tap your steel plates for your couplers to fill and monitor. They would be thick sides at approximately 750psi.
Since I don't know what the cyclic variables are, I am at a loss for what you need. Tires max out at 140 to 150 psi that I know of, so you could make concentric rings of increasing pressure to get your envelope but size may be an issue.
