My moisture level under the house is to high and rotting my underfloor. I've contained one problem with rain water running under my house thru the fondation with a sump pump. All of the old (20 Yrs.) ventilation is condensating causing more moisture and the trunk line is stacked on top of on another down the middle of the house. This is not letting my crawl space vents do the thier job. I'm trying to work with a contractor to put a new trunk line in side by side to allow ventilation from one side of the house to another but he seems to think since I have a over/under unit that it will be difficult. I also have to install vent fans, but don't know how many. I have about 1500 sq ft of crawl space. Any help would be appreciated.