a few units i cut out some thin cardboard (the type for frozen pizza boxes) in the right shape to  fit well on the gap of the antminer and try to improve the airflow going through the entire length. It works, but I really want to make myself some exact measurements and make more of them properly using thicker cardboard or even some very thin plywood/plastic that will be less flimsy.

the satck of 3 units just has a big box lid pressed against it, held in place by the power supplies. it does a nice job at getting the temperatures down slightly. I plan to add to these stacks a little bit soon once i figure out some more power supplies that use PCIe cables (since when stacked the screw terminals are inaccessible)