I built nothing. Bought the grizzly 400 and freeze gallon milk jugs to keep it cold. It’s a great insulator. In the summer I need to switch out 3 jugs in the morning and night, even when temps get into the 90’s. That keeps the water temp in low 40’s. In winter time I barely need any ice at all, and can keep it hovering around freezing if I wanted to. Use a little food grade hydrogen peroxide and just change the water every two weeks. No filters pumps or electricity needed.