I live where it's hot and humid in the summer (like dripping in sweat humid) and still manage to conceal full size handguns (4" K frame, Glock 17) with ease. I wear a tucked in t shirt and over that a loose fitting button shirt. IWB or OWB, makes no difference. And I always have at least one extra magazine or speedloader pouch on the belt as well. No one can tell I am armed unless I want them to know.

In addition dressing around the guns, I only buy holsters that work for my body type and top shelf gun belts.