Lesgold: I run self-made screen bottom boards with a plywood slide underneath all year long on my hives. Only one hive is in a really hot location, so I pull the slide out about 4 inches in summer to give them ventilation when they start bearding. I live in Idaho, always dry, but cold (foot of snow 10F) in winter and hot (around 100F) in summer.
I do not use SBB for mite control. I like the SBB because I can pull them out and tell a lot about what is happening in the hive without opening it up such as whether they are making wax, uncapping cells, eating their sugar in the winter, etc.
jimmy