I'm one of the lucky ones, I get to work physically outside all year round.
Summers in SE PA are much like the south, high humidity and 90's-100's for temps.
If you carry a Glock, your pretty well ahead. The only thing that rusted on mine was the slide stop. I wasnt a Glock fan, (other than their finish) so I tried to get Glock to refinish some of my other pistols, but they said no. To bad too, its probably the best finish out there for firearms. So I had to adjust.
Blue guns and leather holsters are not your friends in the summer, especially if you sweat a lot. Leather stays wet and so does your gun. Blue doesnt last long in a wet holster, park isnt far behind.
Hard chrome / stainless and a kydex holster are the way to go.
If you carry IWB,(my preferred way to carry) the kydex is impervious to sweat, and is very nice to your skin if it should happen to meet it. Wet leather on the other hand, quickly rubs you raw. Kydex is also very easy to maintain, a little soap and water, rinse it out in the sink, and towel dry, and your back in business.
Hard chrome and stainless will rust, so you do still need to care for them. The only place on my guns that tend to get damp and have problems are around the grip, where the holster doesnt cover and wet shirts tend to rest. Other than that, nothing.
If you work in an office, or have the luxury of air conditioning, and dont work up a good, soaking sweat, you can get by with the prettier guns and accessories. If you carry day in and day out, in all manner of conditions, pretty doesnt hold up long, and function is king.
If you like the way you gun and leather holster look now, dont carry them.