Ah!
Much clearer now, BC v BRe!
Many thanks gents very helpful.
My boat has factory fit halyard bags in the cockpit, and they use the twist toggles to which Bob refers.
Bob, a couple of additional questions please if you wouldn't mind?
What is the gap between the hull skins, approx? ie what max length of screws to use safely?
Fancy i might use a timber rail,with glue/sealant so as to give me a bit of versatility in fixing points. Do you see any issues with this?