I've allways thought of it this way, tubes are not air tight, thus the reason the cigars will not stay fresh indefinitly, cigars can and will dry out in a tube. So, If the air can escape it has to work both ways, shouldnt our cigars stay humidified if kept in a humidor. . I may be way over simplifying things, or I could just be way off the mark.
Min Ron NEE suggest storing your tubos sealed, he mentiones that the tubes actually make for a slower but more refined aging.
Just my
take it with a grain of salt.