I normally cut a slot in the plywood false keel and epoxy a nut into it.I then use 4mm threaded rod through the base of the stand,pedestal,and keel through to the nut.I realise this will not help if you have built the model.If you are retrofitting,you are going to need a very accurate pilot hole that extends well beyond the planking.The screw needs to go as deep as is possible otherwise if the model is knocked accidentally you may end up with the keel splitting on the bottom edge.
Kind Regards
Nigel