
....i have drilled into the liner as many times as i need, and almost anywhere i want.... if it pushes in with a bit of give, it is not against the hull, and there is some space behind it for a screw point. If near one of the access holes, or light fixtures, or fuse panel, you can use bolts with nuts, but just screws alone hold well enough, if they are short enough and thick enough to grab the thin fiberglass. I first drill a small pilot hole,
and gently so i avoid the "push-thru" to the hull, and then probe the space behind with the drill bit out of the drill, to see the max reasonable length screw usable. Then drill the hole to the needed size depending on the screw diameter, just a bit smaller than the screw shaft not including the threads, (a screw gauge helps here.) Then use a larger drill bit to wear away a bit of the gel-coat around the hole so the screw does not chip out a piece of gel-coat around the hole, and then use 3M 5200 adhesive in the screw hole, on the threads, and on the fixture of item you are fastening to the liner, to add a bit of extra bond and keep the screw from vibrating loose or backing out. The little holes can someday be filled with putty, 5200, or resin and gelcoat if you are concerned about them, or even drilled to the standard plug size and plugged like the others in the headliner, and besides, they are no real problem. The boat can't be kept looking new forever, and will better serve you if it is equipped the way you want, than by being bare just to look unmodified. The stock fixtures are already put in holes in the liner, and among all those plugs where the factory had to access the bolts to fasten deck fixtures, what's a few more going to hurt. It's your boat, not to be feared.
One of my future mods will be to install snaps along the upper edge of the lower liner, and fit thin carpeting to that flat lower band around the cabin, which can be removed for cleaning, access, or decor change if/when needed. Like the M interior, but easily removable and renewable.
....more holes, but filled with what i want.