Refcreened bottom boards.I started beekeeping using sbb with oil pan. This was kinda new (oil pan) when I started. I keep the pans in 12months a year. Pulling the pan without opening the hive can tell you a lot about what's going on inside without cracking the lid. The years I have been keeping bees I will have to say the oil keeps shb in check and have found many different critters in the oil I may not have known about without taking down boxes and looking. I now build my own bb with oil pan. I have 30 or so hives and for me,I wouldn't put bees on anything else. Only my opinion and what works for me