I'm going to be installing a few new outlets in my kitchen above the upper cabinets for my wife's collection of knick-knacks and holiday decorations, which involves installing 2 new boxes in the exterior wall. I know how to install old work boxes, but I'm stumped when it comes to sealing the boxes to the vapor barrier. The existing boxes have the gasket at the lip and the butyl tape sealing the wire penetrations, but I've never seen an old work box with those features. Will those cover plate gaskets work for something like this? Or is there some other option that doesn't involve removing more drywall than necessary? I'm ok at drywall repair, but I'd rather avoid it if possible. Thanks in advance for any suggestions.
Honestly using a gasket under the cover plate is pretty much the norm when people are concerned about air infiltration. It is very rare to see measures taken beyond that. You could add some loose fill fiberglass insulation (loosely, not tight-packed) behind the box if deemed necessary once you get in there. On new construction they sometimes use expanding foam around boxes, but extreme caution must be taken to ensure that no foam is present in the box itself when completed. A little penetration of the vapor barrier is not a problem in my opinion...Unusually tight construction doesn't allow the walls to breathe and that leads to more harm than good in my opinion.