Help I have mildew!
We have a similar problem, but haven't found a good solution yet. Our house is a walk out, which varies between 3/4ths underground on one side, to completely open on the other. It is great for energy saving, but horrible with mold/mildew. Pretty much anything that gets left on the first foot above ground will get moldy smelling.
We built a passively cooled house in the Piedmont of NC, meaning no AC for our humid, hot summers. Last summer was our wettest by far, and the worst for mildew. I find it on woodwork, clothing that isn't part of the regular rotation, and leather items (the worst!).
I find that woodwork that is sealed well with varnish doesn't get mildew, so I re-coated some of the worst doors/trim last winter. Knots in the wood seem to be the worst. I've been trying to eliminate our leather items and keep pantry items in snap-lock "tupperware" type containers, sometimes with a humidity packet thrown in, or some rice in a sachet.
Mostly, I just did A LOT of cleaning - wiping woodwork down with vinegar or bleach solution, airing or re-washing clothes, etc. Every week, I would make a clean bucket of a bit of soap, vinegar, and water, then put about 20 rags in to soak. I'd pull out a rag, use it as long as I could, then toss it in the washer and start fresh with a new rag. That way, the mildew junk didn't just get spread around.
It got so bad this year, that we bought a de-humidifier. However, it put out so much heat that we just could NOT tolerate it. I think some years will just be worse than others! Probably storing rain-water wet items in a closed up space made things a lot worse than they will normally be. I try to make certain that things get absolutely dry before they come back inside. A couple times per summer, I wipe down our books with the vinegar/water, then sun them before re-shelving them.
My in-laws have a cabin that stays shut up, and they like putting little pots of a product called "damp-rid" around. However, since we open the house every night to cool the house, they haven't worked for us.