If you can access the back of any GRP panels then you can epoxy a small plywood pad in place and then screw or bolt onto that.
We had a pair of eyebolts on the forward bulkhead fitted that way on our World and much of the loose stuff was attached to those with a lanyard.
In some cases there maybe suitable re-inforcing blocks already moulded in place – check with the builders for where those are.
There are 2 options if you cannot easily get to back of most of the GRP panels, and there is nothing already there.
Epoxy a wood pad on the outside face – then screw into that. This works pretty well for things like anchor chocks. Remember roughen the gel coat thoroughly.
Last resort is to drill a hole and back fill with epoxy – as much as you can force through – to build up a mass behind the grp that you can then screw into. Personally I would avoid this unless you really have no other choice.
Hope that helps.