I'd like to put one of these in my head area as well, but I have a hard plastic headliner in my Pearson 30. Anyone installed one in a situation where the deck and headliner have some space between them? I called Nicro and they said they used to sell a sleeve for this but don't any more.
I don't think that would be a problem. The sleeve of the vent is plenty long enough to cover the space. The only Q would be attaching. If through bolting is not necessary, then, once the hole is cut and vent positioned, you can put screws into the fiberglass. Or if through bolting is necessary you could cut some sections of wood to fill the gap where the bolts would pass through. Just need some small pieces to put the bolts through. Again, the sleeve of the vent is about 3" if I recall.