I'm assuming you're asking about a sealer for the inside of the tank. There are many who use a product called Kreem. It's been around for a long time for sealing fuel tanks, especially steel tanks on motorcycles.
I did some reaseach and found a product I believe is superior to Kreem made by KBS Coatings. In their text they say that tests have shown their product is compatible with ethanol fuels where some of the others have shown signs of deterioration after prolonged exposure to alcohol.
I've had very good luck with the KBS product. http://www.kbs-coatings.com/tank-sealers.html