hi,
i have quite a lot of experience with cameras in rio (hasselblad, M8), in various seasons, from zona sul to deep into the favelas rocinha and maré, but never had any problem with humidity
as long as i use leica (more than 25 years) i wrap my cameras and lenses in chamois leather and put them together in any bag - nowadays in an inconspicuous backpack
the chamois leather will not only protect the lenses when they bump, it also protects them from humidity and takes the grease and sweat from your hands
have fun and don't wear your camera like a piece of jewelry!
sam