I have lived in the humid southeastern USA for the past twenty-five years. I always wear a cotton T-shirt between between the gun and me. I find that not only does the gun stay drier, I stay cooler. Yesterday it was about 88 degrees and 60% humidity when I started some auto maintenance and yard work. When I finished, it was 92 and 56% per my wife's weather station. I wore my G17.3 in a Sparks VM-2 between a polo and T-shirt. Gun was mostly dry, but I had sweat through my underwear and pants. The T-shirt absorbed much of that moisture.
As for protecting the pistol, a hard paste wax like Johnson's or Renaissance Wax will do the trick as long as the surface is polished. Matte surfaces tend to get uneven wax distribution whereas even coverage is simple with a polished surface. This is the low-cost way and works for up to a few months, depending upon how hard the pistol is used. Another method is to use something like G96 or a Sentry Tuf Cloth to provide some protection from sweat. The higher cost method is a corrosion-resistant finish like NP3.