Ran the type of bottoms with a slide in tray for a while, the robbers are liking to find a easy way in, then some of the hive was hanging out by tray slide fighting them off, ended up with 10 or 20 dead bees a day in a couple hive's trays, yanked those suckers off & threw em on the burn pile, the trays come in useful for trimming wild comb tho.