I’m struggling to remember exactly- it was on another club’s boat and I only sailed it once. I don’t think it was on the centreboard case. The boat was a MkI so perhaps it was on the aft face of the deck moulding (the part that makes a sort of ‘arch’ shape). On a MkII you could probably put one on the buoyancy tank bulkhead. And a floorboard would offer the easiest place of all to mount one- maybe tucked underneath the front benches? The tabernacle could be an option but it might end up getting tangled with your halyards.