Most of my childhood and backpacking was in MD/VA/WV. As an adult, I was a long time resident of San Antonio. I now live in the Missoula area were humidity in the teens or single-digits is common. Color me very, very happy.

So I don't have a storage problem but my approach to powdered drinks on the trail could help with your end results. I baggie package individual servings (or maybe two) of a mix of Carnation Essentials (nee Instant Breakfast), Nido, and instant coffee/expresso. To mix these ingredients and to avoid clumping when preparing the beverage, I use a sifter when packaging. It nicely mixes the stuff and on the trail and I get no clumps when adding the hot water...

FB