Mine is screwed on with SS countersunk self threaders. The screw heads are plugged over with the same wood. Just make sure the screw holes in to the buoyancy tanks are well sealed, for example with Sikaflex. Plugging the screw heads is easy with polyurethane construction glue (the type that foams). Hold the plugs in place with some adhesive tape while the glue sets. Then sand the plugs and varnish. It is as easy as it sounds. The P-clips on my boat are fixed using the same screws that are used to fix the rubbing strakes.
Any extra weight should be taken of the lead beneath the thwart. A certified boat has to meet minimum weight requirements and if you remove the screws from your rubbing strakes you may have to add lead to the thwart.