I recently moved from probably one of the toughest areas of the country (south of Houston) to keep the mildew from forming on the trim. This what I used and it worked well but had to stay with the program to keep the stain off. I would mix one ounce of "Consan" with one ounce of bleach in a quart spray bottle and soak the trim about once a week. Never scrubbed or wiped down and my trim is a clean and bright as the day I pulled the Montana off the lot three years ago. Check this link, it can be bought a such places as nurseries and farm supply stores.
http://www.consan20.com/