Does anyone have a recommendation for sealing galvanized ductwork? I've read that mastic is the best, but looks like it might be a bit of a mess. Tape seems easier, but I've read that most don't perform very well. Any thoughts? What about a specific brand of tape that is approved by most building codes (UL-181) for use on metal ductwork? All I seem to find at most stores is UL-181 approved for ductboard or flex duct, not metal.

Thanks for any help,