Several of us on this Beemaster site use a double screen bottom board. We place a pan with oil in it between the screens, this space is bee proof and I usually have a pan that is smaller than the screen, this allows air to flow. To make the dsbb more attractive to beetles I place a blackout over the bottom screen and then place the oil pan on top of this. I use plant mulch cloth on a frame like a top board for the blackout, I only go to this trouble when SHB are bad, after the beetle population goes down I remove the blackout. I use the oil pan on all my hives, this is not practicable for large a commercial BEEK. This summer I am going to make top board with the screen wire and a spacer to allow more air and let light in the top, which makes the top of the hive more unfriendly to SHB.