A friend of mine in Washington uses a ssteel 300 gallon milk cooler for a fermenter. They are stainless steel with two lids, no seal. He does a single malt whiskey. I just picked up a similar 500 gallon jacketed cooler that I will be fermenting my rum wort in. They are nice as you can add an agitator, mine has two coils in the jacket. I will use one coil to heat and the other to cool with. They can be readily found in various sizes on craigslist and other ssteel tank dealers.