Shot this a while back, but I thought I'd share one experience I had while visiting a rain forest exhibit. Temperature was cold outside and then stepping into the exhibit the camera immediately fogged up. Even though I wiped the lens down, it continued to fog up. It actually took about 15 minutes before the gear acclimated to the right temperature. This all happened before I was able to take these photos (seen here).
I've worked with cheaper non resistant lenses and the moisture can actually get INSIDE of the lens. Once that happens you'll need to go through some steps to get that moisture out, which is not easy. Moral of the story is to know what you'll be getting into and bring the right gear. The GH3 body has been redesigned to be more weather resistant and i'm using the 12-35mm F/2.8 Dust and Moisture resistant lens.
Panasonic 12-35mm F/2.8 Lens