Best camera for backpack style traveling?
-Needs to be able to handle humidity, but not necessarily needing to be weather sealed.
It is my experience that humidity is a bit of a problem unless you are using a weather sealed body and lens. I haven't had too many fogging issues, but I have found high levels of humidity is often better at penetrating then light rain.
The smallest sealed body and lens combo is the Olympus OM-D E-M5. Since you already have some lenses and bodies, maybe consider the smallest sealed offering within that brand instead?
The other option is to compromise on image quality and get one of the small "tough" cameras which can be used underwater to a limited degree.
See my plan (in my profile) for what I shoot with. See my gallery for images I find amusing.