Just for everyone's benefit, in order to rid this problem, it needs to be attacked from its source.
Lack of sunlight and lack of airflow and excess/residual moisture are the main culprits contributing to this problem. If you improve these culprits one at a time, starting with the removal of the excess moisture, you should see results relatively quickly. If water is pooling anywhere, even in the grass, as it evaporates, it rises and adheres to the vinyl. Then, under ideal temperature conditions, mildew begins to grow. Once you've done what you can to the landscape to drain/remove excess water (all around the home), it's time to improve the air flow. Trim back your trees and bushes. Shrubs should be 3' or more from the home. This allows moisture to rise and get pushed-out by the air. If the problem persists, you now need the help of the sun to dry out the damp areas. Since the sun is a fast dryer, as the moisture evaporates, the sun heats it up as it rises.
As mentioned, the best thing to do is all 3. In this type of situation, whether it's humid a lot or not, moisture will condense if the air and/or surface around it are cool enough. If the side(s) of the house in question are in the shade (especially), cool surfaces abound! That's why grading and removing excess moisture, pruning, and heat are all necessary to eliminate this problem. My best to ya and hope this helps. BTW, if you have objects such as decks, sheds, fences, and the like real close to the house, air doesn't move too well around them. Take a look at these types of 'obstructions' to see what you can do to improve air flow and sunlight.