I currently own a Big Agnes Lost Ranger 15 bag, and it is the previous version, not the new one with water-repellent down.

I am getting ready to leave on an 11 month backpacking trip to 11 different countries. I am nervous about my sleeping bag in some of the countries in Africa and South Asia. Instead of forking out the $300 for a new water-repellent down bag, is there another option? Can I sleep in my sleeping bag also inside a waterproof bivy sack? Does anyone have experience dealing with down bags in humid and wet conditions?

Any help would be greatly appreciated!