Dmorris,
You don’t need to drill holes for air exchange. Air exchange is creating the problem in the first place.
You are right in assuming that the black color is aggravating the situation. During the day, the toolbox heats up. The air inside expands and forces its way out of the box. At night, the toolbox cools down and the air inside contracts, sucking in fresh air.
The air that’s leaving during the day has had its moisture condensed out the previous night and the fresh air that’s entering the box at night contains a full compliment of humidity. As that fresh air cools, you get the liquid water inside the toolbox again. This will happen every night as long as the temperature fluctuations and humidity are sufficient to create the condition.
This is also how fuel and other tanks get moisture building up inside them over time.
For what it’s worth, you are probably also getting condensation inside your doors and other body panels at the same time.
The best solution is to park the truck in a garage. Since you are full-timing with an RV, that’s probably not going to happen. The next best thing is to park under a carport or other cover to prevent the daytime radiant heating and nighttime radiant cooling. If that is not an option either, you should at least throw a tarp or other cover over the box whenever the truck is parked. During the day, it will help prevent too much of the dryer air from being forced out of the toolbox, and during the night it will help prevent the toolbox from getting even colder than it does now.
Another solution would be to provide some sort of heat inside the toolbox during the night. This will prevent the air from cooling to the dew point, which is the temperature at which you start getting the condensation. You could use something as simple as a lightbulb or a VERY SMALL heat source. Be careful not to choose something that may produce enough heat to start a fire. And be sure you unplug it before you drive the truck away.
Best of luck,
– Loren
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