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If the patent wasn't denied, it should have been. Military "explosion safe" fuel tanks have been made that ways for ages. the tank contains either a foam rubber filler, or a metal mesh filler, which completely fills the tank. The metal mesh absorbs heat, preventing combustion if the tank has been penetrated by live rounds.
Nothing new here. You DO, however, need to wiggle the block into the tank (easier before assembly) and make sure the components are fuel-proof. And for boats--engineer a well for the fuel sender float, and consider that you will be creating a "honeycomb" nest where dirt and critters can accumulate.
Things are a little different for combat aircraft.