The best solution I've found is to convert your old solid bottom boards to tops. Turn them up-side-down with the entrance reduced installed. I use bottomless hives, my brother uses screened bottom boards, the solid bottom boards are the best tops I can find, air vent and top entrance all in one, no shimming required.
Ok Brian, You got my attention with the bottomless hives statement. Could you please elaborate?
My hive stands are made thus: I cut a piece of 3/8 plywood 1.5 inches wider and 1.5 inches longer than the hive body it will support. I then cut a 1X3 1.5 inches wider than the hive body. I then secure a 2X8 to each long side of the plywood sheet. The 2X8 is 1st notched 1.5 inches by 3/4 inch at the top to fit the 1X3 so that 1 inch rises above the top edge of the 2X8 in a |_______________| fashion. I set a slatted rack on the newly made hive stand and secure it with screws to the 1X3 with 4 screws. The hive bodies are then stacked on top of the slatted rack.
The bees do not land on a landing board, they fly in and out both the front and back sides of the hives. They fly right up into the hive past the slatted rack and the excess bees festooning from it. Any predators has to crawl unto the hive stand where they are attacked by large numbers of guard bees.
I must admit that my bee yard, like all my other fences is 6 feet high, 3 rail, 2X4 welded wire so most predators do not bother my bees as they have to get past 3 such fences to get the bee hives.