Water is one thing, humidity is something different because it can directly have an effect on load performance during and after the load process. Chronoplotter. If I recall correctly, there's ~ 29fps difference every 10% humidity. Powder burns by weight, not by volume. So I think it really depends on what your intentions are. Range time with the 223/9mm etc.. probably not so much. If you're shooting F-Class, Benchrest, ELR or even PRS, these numbers mean something totally different.
I personally don't seal my rounds. I control the humidity in my loading room and for each container of powder. I generally load the night before I have a match so my loads generally don't swing in velocity very much.
Chronoplotter has done a significant amount of research on the subject of humidity, loading, and shooting. So if this sort of thing interests you, his research is free to read.