I had the fill plate off for installation of a capacitance type sender (no more factory sender for me!) and the blocks looked fine after five seasons of pump gas.
That said I do use a filter sock around the end of the in-tank pump. You DO use an in-tank pump, right? (YOU probably use TWO or THREE in the tank, Ed, I know you do.
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CAVEAT: If you go to remove the foam be very careful around ignition sources-- when you pull it from the bladder fuel will spray in the air. Be certain the tank is absolutely empty and even then, exercise caution. It would not be unreasonable to fill it with water prior to performing any maintenance. Just be sure you can dispose of the water in the appropriate hazmat site, don't just dump gasoline into your ground water.