I would like my contractor to insulate and seal the hard duct that will replace the existing flex duct in my crawl space. I mentioned mastic to two contractors. One seemed not to be familiar with mastic but said he could use a hvac caulk. The other seemed reluctant and when he submitted his estimate he specified that he woud tape the joints. I assume he will use foil tape. In other old posts I have seen a wide variety of opinions on foil. Is there a foil tape that won't fail after a few years? Is there a mastic tape that is really durable? Can insulation be pulled over wet mastic? Does caulk work?