Sick building syndrome is not a problem with any particular builder or unique to manufactured homes.
"Sick building syndrome (SBS) is a combination of ailments (a syndrome) associated with an individual's place of work (office building) or residence. A 1984 World Health Organization report into the syndrome suggested up to 30% of new and remodeled buildings worldwide may be linked to symptoms of SBS. Most of the sick building syndrome is related to poor indoor air quality....
In hot, humid climates, moisture is the primary culprit.....
The uninformed or poorly informed assume that the air conditioner will successfully remove such moisture, and it may if it is operating efficiently. Many air conditioners do not, and almost all of them decline in their ability to dehumidify efficiently over time. Residual moisture remains and soaks into materials as if they were sponges, on a march toward full saturation. In hot, humid climates, the worst months for mold are October, November, December and early spring...when air conditioners rarely operate and moisture saturation increases most rapidly.
Identification and termination of these unintentional building matrix airflows has rarely been recognized and acted upon, hence heroic efforts to heal the sick building have been largely unsuccessful. Out of a sense of frustration with enormously expensive and ineffective healing approaches, total building destruction is sometimes selected as a way out.
With proper application of currently available instrumentation, identification of unintentional building matrix airflows is relatively easy, quick and inexpensive for a knowledgeable, experienced, building science practitioner. Pressure and micropressure management can result in immediate odor and toxics distribution system termination. With application of correct technology, and often without installation of any additional equipment, relying only on what is already there, within hours of completion a sick building can begin a gradual drying out process to heal itself completely."
Source:
http://en.wikipedia.org/wiki/Sick_building_syndrome