It's impractical to keep the boat air-conditioned which is just dehumidification followed by air cooling. Within minutes of opening it up you're going to have an equilibrium between outside conditions and inside conditions. And even if you kept it buttoned up, it's going to get awfully hot in there later in the summer.
I suspect that the seasonal weather is playing havoc with you. Damp spring air is what cause me the biggest mold and condensation problems here in Michigan as well. Good ventilation is the only really effective way to keep ahead of it. In short, you apparently need more flow.
If you've got good ventilation while you're using the boat, and you button her up at the dock in low humidity conditions the desiccant might keep up with it, especially in the warmer summer water. The cold water against your hull now causes the warmer moist air inside the boat to drop below the dew point as well.
I'd focus on getting more ventilation. I don't think anyone will disagree with me in saying that you cannot have too much ventilation on a boat.
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Wm. F. Buckley, Jr.