I use a similar setup as your stock tank except mine is galvanized. We knew we had cold, Oregon winter weather so my husband cut out 2 pieces of plywood the shape of both ends of the stock tank. Then he nailed a lip onto the outside of the plywood making a lid. These 2 pieces are cut so that the heat lamp hangs down in between the plywood leaving an opening in the top big enough just for the heat lamp. I will post a pic when I get home tonight. I don't think a wire top will keep enough heat in for a 32 degree night.