87 Mako 20' removing the fuel tank(tech support john cobb)

this boat is 30yr old, has gotten corrosion underneath the tank. I wondered why it always had water & crud in the filter? I had to change the fuel filter every time i drove it. going to have a smaller tank made, since now engine is a four-stroke. Don't ever foam in your tank, put neoprene rubber under & sides to snug it in. Thanks for the good advice John