The cans I show above were pristine inside, unused. The outside was a bit dirty and had a couple rust spots from storage and paint damage during transport. I wire brushed them and painted them, but would have been completely comfortable just filling them with gas and storing them as received, for a couple years no problem.I've considered buying old ones, bead blasting them inside and out and powdercoating them. Inside and out. Got the blasting setup, but never done any powder coating.
I use ethanol free fuel with a double dose of Stabil. Ethanol fuel, all bets are off.
If you haven't seen it yet, this short documentary is worth a watch: