The "Rycote" Duck works great for rain....
I have used them even on heavy rain for fixed field FX on golf and football, but they would be useless on a boom pole. http://www.rycote.com/products/214101/
As for dust protection I tend to rely on the fluffy windshield and its multiple layers of fabrics.
Another version is the "Rainman" I've never used it but it may be better for pole use. http://www.trewaudio.com/remoteaudio/rainman/
The difference between Knowledge and Wisdom is... Knowledge is the knowing of facts.... Wisdom is the sensible application of good quality knowledge...
Not to put too fine a point on it - but for as long as I've been around audio, my studio toolkit has included a few non-lubricated - non-powdered "plain vanilla" condoms specifically for slapping on shotgun mics if it starts raining.
Not only is it ideal mic protection, but making the trip into the drugstore was excellent training for my son when he was about 16 - he was typically mortified at the whole process - but overcoming those particularly nerves early might just save his life someday.