Welcome to the site, though I am posting this somewhat late! I too am in Mount Vernon...small world. I built a concrete block arch lined with brick that supports three steam trays. In conjunction with a stand alone warming stove with one tray I can do 60+ gallons of sap in a days boil. We had 18 or so taps on 2018 for 7 gallons of syrup and are looking to do 24 this season. No problems with the blocks cracking as the brick keeps the heat down. Besides at $1.65 each it's cheap to repair.
Best of luck this season!