DEHUMIDIFIER....ventilate or not ventilate

[sailingabe41ds]

Hi..

I keep my boat in So Cal....dry air, keep all ports slightly open for ventilation and no dehumidifier. Never had a problem. In the next few years planning on moving to the Pacific Northwest. I read on a similar thread about having to keep dehumidifier on every day to prevent mold/mildew. Shouldn't you keep the ports all closed? If you keep them open for ventilation ...aren't you just getting more moisture from the outside?

What do people normally do in areas similar to the Pacific Northwest?

Thanks in advance....I may just be overthinking this.

Abe