Ok those crappy fridges take like a day to cool down, and like 4-5 days to get to freezing temps with no one opening them while on high. So right there concept toasted.
Rather then keeping moisture out of the air perhaps you can do what everyone else does and make the componets water resistant. Theres even a spray for this, you'll have to cover things you want to use later, like sata connectors, or PCI slots.
Condesation forms on colder things. Go get into an air conditioned car, stick your face into the vent and see how long it takes condesation to form. Have you ever steped into an air conditioned car and thought the seat was wet from the A/C, no..... I hope not anyway. Open the fridge and grab a can of soda, as long as the fridge hasn't been open a while you can grab the soda and it'll be dry, 5 minites after you take it out the moisture in a warm room will collect on the can. The only way he would have a problem with condensation is if he had some air coming into the case without going though the cooler/fridge/ac first.