If I were going to do it, and I'm not, I think I would pour some concrete tanks and plumb them. Size would be dependent on your goals but it would be expandable by pouring another vat next to it/them. A thermostatically controlled propane water heater should suffice along with something electric for aeration. A heater that assured a level, cool temp could be the real key. If you had several, one could be drained for periodic cleaning.
