While on a past vacation in Florida I carried my Glock 22 in a Glaco IWB holster. I wore shorts, an undershirt, and a short sleeve button up "tourist" shirt. I didnt have a problem with it. I am glad I had it too , thanks to our willingness to carry our firearms, our car didnt get stolen, and a car thief got a first person lesson in military tactics.
My most recent vacation to Florida I took my Glock 21 SF and my Glock 30 SF. I tried carrying the 21SF, but I guess I am getting old because it didnt feel right. The 30SF was the answer. I dont really like to compromise firepower for comfort, but I am different.
The over shirt is my answer to carrying full size pistols. SHoulder holsters are also a good investment. When I buy polo shirts, I usually get them one size larger and they seem to cover up well. Using these tactics have worked well for me while in hot and humid climates.