Our home is built into the side of a slope with a crawl space. Floor joists are insulated with batts & ground covered with poly. Crawl space turns into a swamp during summer! Downspouts & grade are not contributory. Source must be condensation from the humid summer air hitting the cool undersides of the house. Foundation vents are on the one exposed wall. Condition has gotten worse as we have added a sunroom which reduces circulation under the house. I am currently running fans with less than optimal results. Should I remove the poly & batts (as the poly is wet on top & underneath & never allows the ground to fully dry out in the winter), replace batts with foam insulation, & then whether to increase air circulation via a forced air duct run from the exposed wall to the back of the crawl space, or as others have recommended, closing everything up & install a dehumidifier? I only want to do this once, & get it right. I am concerned that running a dehumidifier would be costly in ongoing energy bills. I need a knowledgeable non economically motivated opinion as to what to do!