For what it's worth, the cabin liner is a piece of TRIM, not something that would ever be designed to take the potential loads of a person being flung through the cabin.
If you really want the rails mounted in that location then epoxy
a piece of hardwood the same thickness as the gap between the hull
and liner to the hull
where you want the rails and screw the rails through the liner to the installed block.
make the block large enough to spread the load that MAY be applied to it.