[Cam]

TRY THIS FIRST. take some simple green and water and drip a small amount down your vents (not the ones above the stereo unless you want to short out your source unit). Hopefully this takes care of your smell.

As for the humidity inside the car, it could very likely be coming from your tail lights. They are known to leak. Check for water in your trunk by your spare. You can fix the leak by sealing them into place with silicone.

Good luck.