Here's how we installed the insulating layer in the cabin ceiling

Polyethylene sheeting that's sold as a flooring underlayment, and the adhesive spray 3M #90 product:

Before - the raw ceiling just inside the cabin (light unscrewed):

Spraying the 3M #90 adhesive on the ceiling's edge (and the light is upside down on Pusser's mug):

Spraying the adhesive onto the edge of the sheet:

Smoothing the leading edge of the sheet into place at the ceiling's edge:

Reinstalling the light (after cutting a slit in the sheet):

Prepping the rest of the two surfaces, because the adhesive must be sprayed on both sides, then wait a minute or two before pressing the sheet onto the ceiling:

Smoothing the rest of the sheet up onto the ceiling panel:

Trimming the overlapped areas:

The result was the much nicer look of the polyethylene sheeting (almost like a bandage!) smoothed over the nasty-looking raw surface that had been left after ripping down the old headliner. We realize that installing the new headliner fabric will be much more challenging. But it's great to have the cleaner-looking intermediate layer in place.