I am building a new house and am looking for a system to air seal the receptacles and switch boxes in the exterior walls. The walls are vertical and horizontal 2x4 with zip system taped sheathing (primary air barrier) outside. There is 2" of XPS on the exterior and the 7" cavity will be filled with cellulose. There won't be a vapor retarder at the drywall layer so I'm looking for a good way to prevent air migration from the interior space to the wall cavity. Most of the systems I've seen use a box around the device box but it requires sealing the box flange to the vapor retarder (which I don't have). Has anyone had luck sealing the drywall to the box with acoustic sealant. Seems getting sealant to adhere to drywall would be tough and not too durable. There are boxes with integral flanges - anyone used these? They run about $4 a box compared to $0.40 for a plastic box.