I have never used cinder blocks ever but one thought popped into my mind when i saw the supporting steel.
Have you considered if the steel can/will leach into the system over time??
It would be so awful to go to all this effort and overlook something simple.
I think if water gets to the steel it's game over anyways. Similar to plywood builds, if the epoxy lets water touch the wood, it is a failed project and what could leach is a moot point.