Hey, Carol. I'm only a couple of years into beekeeping, so take my statements with a grain of salt. I am also in Florida and I figured that the bees would need some ventilation to cope with our temperatures. What I observed was just the opposite.I didn't use top ventilation, but I started my hives on screened bottoms and quickly noticed that the queens would not lay near them. Wondering if the lack of temperature regulation was the cause, I moved half of them to solid bottoms and the laying pattern improved greatly.
Some of my hives are still on screened bottoms, but they are not as productive or as populated as the ones on solid bottoms.
I also can't tell that the screened bottoms help at all with mites or hive beetles. Matter of fact, I have some hives on solid bottoms, in the full sun, and these do not have hive beetles. None at all.
I'm not telling anyone not to use them, I'm just saying that I have not found any benefit from them. The only bottoms I build will be solid, at least until my observations prove to be wrong.
I personally think that the whole ventilation thing is overrated. I never saw a screen on a tree.