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I think the best bet would be to build a walk-in environmentally controlled room that would not only cool, but heat also, especially if you plan on having more than one of these.
1- 55 gallon stainless steel drum
(i used abby drum in Baltimore Md) BUY USED
Have you considered an interior stainless chiller attached to the lid. Make it about half the diamater of the fermentor. It would come off with the lid so could be cleaned and would not touch the sides so no worry about scratching your fermentor. Then have an external wrapped around the outside. This would help distribute cooling throughout the beer in the fermentor. No warmer spot in the middle.