The box that Mike was using in his demonstration is also known as a Vivaldi board. It is a multi-purpose piece of equipment that works quite well in our moist, Pacific Northwest climate. The sides can be 4 to 6inches tall, with a 2 to 2.5 inch hole in the center and screened vent slots on the front and rear ends. It usually has a removable screened cover for the center opening. It can serve as an insulating box, a moisture control box, and a top feeder.
The edges of the hive top, when in place, will cover, but not block the front and rear vent slots, allowing a slow flow of air out of the top of the hive. Placing a burlap bag in it allows moisture to condense and evaporate outside, away from the frames, resulting in less excess condensation within the hive. The bees will control the size of the center opening (and hence, the airflow) by using propolis. It's advisable to have an extra burlap bag available for exchange, if the one in place becomes too wet.
During cold weather, you can pour dry sugar through the screened cover to feed the bees. During warmer weather, with the screened cover removed, a feeder can be placed inside the Vivaldi board, over the center hole and filled with sugar syrup to feed the bees.