Cabin pressurization is a necessary evil for airliners and nothing that a designer wants to deal with. The original Boeings had the benefit of being designed while Comets were exploding in flight. They put a lot more time into their fuselage because of it. Everything was fine until a 737 popped its top in Hawaii. After that, the FAA began paying a lot more attention to older aircraft. The entire fleet got massive doublers/patches around the L1 and R1 doors and an ongoing NDT program. DC-8 and 9 fuselages are much stronger than Boeings, they are limited more by damage than fatigue cycles. The fuse skin may gain some compression strength while pressurized but it doesnt matter because the only time it actually buckles is on hard landings. The 787 fuse is actually heavier than a metal one. Once enough material is added for omnidirectional strength and allowable damage, it is very robust. This along with excellent fatigue life of composites allow the cabins to be pumped up a little more without penalty. As far as moisture, yes, airliners are wet and nasty under the interior. Lav and galleys stay saturated and smell like dumpsters, lower insulation is usually full of "blue" water. You all should change a cabin air recirculation filter to fully appreciate your work environment.