Mixing of powders is not a good idea at all, but when you pour a base of Goex down, then level the load and pour your Pyrodex, APP, Pinnacle, Triple Se7en, or what, I see no harm in it. All the Goex is doing is creating that burst of fire and heat that the substitue powders need.

If humidity and condensation is the problem, that is a whole different animal. Even a duplexed load will fail if subjected to conditons of barrel condensation and humidity.