About two years ago the duct work was replaced due to mold. Reason given for the mold was the fiberglass supply duct exterior coating had failed allowing moisture to saturate the duct over time. The home is located in coastal North Carolina, has a crawl space sized for a very small person. The Trane gas pack is new about three years old. All the work has been done by a local HVAC firm that has been in business over thirty years.
Recently while doing some work in the crawl space I inspected one of the supply duct connections and found air leakage at the termination point of the fiberglass duct to the floor box. The leak was also causing condensation to form, which was running into the duct. The connection is made with a Panduit strap. The metal floor box has insulation wrapped tightly around it. Inspection of several other connections also revealed the same issue, supply air leakage resulting in condensation running into the duct creating mold.
What is the proper sealing method to prevent this problem?