Condensation isn’t the issue, at least not in the way you might think it is.
“''My humble conclusion is that, the Macbook Pro (mine is a 13” mid 2012) is prone to condensation due to its very high operating temperatures (hot air holds more moisture than cold air) caused by its enclosure and low rpm exhaust, plus, its cold aluminum unibody, making a perfect place for condensation to be created.''”
Condensation occurs when moisture present in warm air meets a cooler surface, but this isn’t what’s happening if a MacBook is left at ambient temperature (''everything'' would be covered in condensation if that was the case) or if it’s powered on - in which case it will obviously be running at temperatures above ambient, ''inhibiting'' the formation of condensation. This doesn’t prevent airborne moisture from causing havoc though, especially with regards to formation of corrosion.
There are two potential options to alleviate this issue.
# Removal of the logic board and spraying with either Servisol “Super 10 Contact and Switch Cleaner” or WD-40. Both of these work to disperse moisture, leaving a thin oily film which acts as a barrier against moisture. They’re electrically inert and from experience will not damage a logic board or its components.
# For a more permanent solution use clear coat lacquer. Again, remove the logic board and warm it up in an electric oven on its minimum setting to drive any residual moisture out. This will not damage the board or components as there’s no current flowing through it. Next, put masking tape over all connector points on the logic board, not forgetting the RAM slots (where present) and the display connector. If the heat-pipe assembly is being left in situ then cover up the radiator fins with a plastic bag as the insulating properties of the lacquer won’t be helpful. This is also the perfect time to remove the factory applied thermal paste and apply some fresh TIM of your own preference. Once all connections are protected and you’re sure you’ve not missed any, move onto the next step. Apply the clear coat lacquer in several thin layers allowing each layer to dry before applying the next. Leave at least 12 hours to harden then reassemble your computer.
Both methods will form a barrier against airborne moisture and will inhibit corrosion. If this seems a little extreme it’s not really when the alternative is paying Apple’s extortionate fees for a logic board replacement, in which case there’s nothing to lose anyway. As it is I’ve tried both methods and they both work, although the lacquer option is a more permanent fix.