Just a quick note to all who worry about, or are faced with replacing failed steel (black iron) fuel tanks. My failures were because of water seeping past failed caulking of the deck fill plates, after 20 years. I filed an insurance claim that pointed to language in my policy that said, after saying all the things that the policy wouldn't cover, that it would cover "hidden defects at time of manufacture." My photos of very spotty caulking around the deck fill plates were proof that had the caulking been properly applied water would not have entered just above the tanks and pooled (on both sides.) Bottom line: insurance paid all but my deductible of a $40,000 bill (including new decking associated with the water intrusion.)
Since anybody involved with boats knows that most boats probably have some kind of hidden defect when built I'm not sure that policies today are written with this language but it may be worth a look at yours.