Re: Hot weather and entrance reducers
You could take a piece of #8 hardware cloth and cut a piece 3" wide by ever how long you want the reducer to be. Fold it and "pinch" it together and slide it into entrance opening. It will reduce the entrance but still allow ventilation. Regular window screen could be made to work in a pinch if you didn't have #8...will just have to make sure the window screen can't fall out easily (it doesn't have the spring action of the #8).
Using the screen will also fake off some of the robbers into trying to get in through the screen and thus lessen the number of them at the actual entrance.
I take it that you are using solid bottom boards?
Warning: Rookie beek...take my postings with that grain of salt you keep in your pocket.