Most late model poly tanks and fuel cells should be safe to use, as they have to be bale to tolerate ethanol blends. Most tanks from 88 on appear to be safe for use with ethanol as long as you don't leave them open to the air for long times with the ethanol in the tank.
I have done a lot of stainless fabrication so I also know what it takes to work with it. I still say it is much more duable, buT I don't feel it necessary to go that far.
Most tin used in the automotive workld is like I said, tin roofing is the same thing, where you refer to tinning the sheet metal. The material in refrigerators I thought to be aluminum, as I have turned it into the scrap dealers many times as such, and never have been told it was tin, the tin classification at the scrap yard is still iron based.They pick it up with a magnet if that means anything... and gas tanks go in the tin pile.