well... we have an underground phone line burried in a trench up the driveway right next to a powerline coming in and every time it rains the phone crackles and buzzes until the moisture dries up so i would say having a cable signal act the same way is not out of the question.
why does it get humid in the room? do you not have the dryer vented properly? we have a washer and dryer located in a 10x7 closed off room without issue. if you do have your system vented you could have a clog in the hose, a leak, or your dryer could be full of lint.
exessive humidity is bad for not just your cable box but could potentially allow fungus or mold to grow and in severe cases moisture could attack the paint, wallboard or wall framing.
i would suggest figuring out why there is exessive humidity in the room instead of trying to bypass the problem, however, this is your choice. you might be able to eliminate the problem with a completely sealed enclosure which is watertight or moving the connection to a new area would work as well. getting a cable re-routed is not a huge deal.