Great idea. I have seen this done a few times with various pressure vessels.
Take note on continued use beyond the 5 year inspection period that requires hydrostatic testing. Think of that as a safety item.
Fair point - with normal working pressure for these at 850 psi and testing to 3,000 psi i feel fairly safe at my 75psi air fill 
did pick the nicest looking one of the bunch though, don’t get some rusted thing a magnet fisher dragged out of your local pond!