I've been looking at this since I've just completing my first recording rig. Consisting of Sennheiser me66(Sennheisers, I've heard, do better with humidity than other shotgun mics), sound devices mm-1, and an h4n just for the recording (if i want ambience, my h2 has 4 mics).
I'm currently living in Japan, and the humidity is just starting to set in right now. In a few months, I'll also be traveling south east asia for sounds. This will be even greater amounts of humidity and heat.
That being said, I've been preparing for humidity. You definitely do not want to be letting the mics go from cool and dry to hot and humid or vice versa very quickly. Condensation may build in the mic from doing that, which would obviously be not good at all.
The ziplock type bag is a good idea, but I'd also wrap it in a towel or some sort of insulation in that bag to help it acclimate more gradually.
However, the most important things to have in that ziplock bag with your mic are some silica gel packs. You know the ones in food packages that absorb moisture to keep food from spoiling? Buy some at a camera store and keep your mic from spoiling!