If the house smells like mold...find the mold and get rid of it! Hot humid air should be kept out of the house. It the house is on a crawl space, the crawl space should not have vents, it should be insulated at the walls and conditioned. The same goes for the attic; the attic should be insulated at the roof and conditioned. All Heating, Air-Conditioning, and Ventilation (HVAC) ducts should be within the conditioned envelope of the house. Exterior walls are going to get wet; provide a drain plain to facilitate drying between the exterior sheathing and exterior finish siding. This is a photo of a blower door test, that checks for leakage in the exterior skin of the house.
Residential architects who specialize in the hot, humid, southern climate