I know you guys will think I am nuts, but the best and cheapest plain well tank, is a water heater. Its insulated, has an anode for long life and lots of ports to work with.
Would likely work for treatment retention as well, but I am not versed [thank god] in drinking water chemical adjustments.
Its a real shame that glass lined well tanks and epoxy tanks do not have an anode. You would get an extra ten years, but the MFG. does not want you to know. I'm going to add a spare one to a sears glasslined and see how it holds up - if I live long enough for it to rust out.