27 seamaster option for Monel fuel tank

[Bushwacker]

Two words . . . WEIGHT & COST! Monel is primarily Nickle, which is much heavier (and more expensive) than steel, not to mention aluminum. You're right in that nothing beats the nickle based alloys for corrosion resistance, but aluminum works just fine for a fuel tank if you install it right so air can circulate around it. I'm amazed at how many boats have foam around the fuel tank, which is the worst possible thing you can do to an aluminum tank, since it holds water against the tank, greatly accelerating corrosion!