Steve my ParkLiner's ceiling is similar, carpet and bubblewrap insulation. Mine had a wooden trim ring on the inside that is screwed up into the fiberglass just along the inside edges of the opening in the ceiling...covered by the hatch fan when it is installed...I kept it the same...are you adding a new hatch or upgradeing? I used the white trim ring from my original fantastic fan...it was a close enough fit.
All that is gold does not glitter, Not all those who wander are lost; The old that is strong does not wither, Deep roots are not reached by the frost.... J.R.R. Tolkien