I don't care what the core
is or where in the boat a screw is put. Drill the hole oversize and fill with thickened epoxy
then redrill for the screw. A self tapper will need a pilot hole just under the larger diameter of the screw, If the root diameter is used it will most likely be too tight and crack the filler material. I would lightly oil
the screw, with spray on cooking oil
, and screw it into the filler before it sets, obviously without the fitting it is going to hold. Undo when cured and you have a very solid mounting.
Maybe overkill but it makes me comfortable