Mold is a problem that is NOT unique to manufactured homes. Owners of homes of every type and size are having problems like yours across the country. Molds are part of the natural environment. Outdoors, molds play a part in nature by breaking down dead organic matter such as fallen leaves and dead trees, but indoors, mold growth should be avoided. Molds reproduce by means of tiny spores; the spores are invisible to the naked eye and float through outdoor and indoor air.
You will find quiet as bit of good information from the U.S. Environmental Protection Agency in their free Guide to Mold, Moisture, and Your Home