Get a router to do the job , can even make up a timber gig for you to place down to make the cut smoother ,
buy the handle then masking tape over the hole part as resin not to fall into the handle itself cut out the hole template then drop the handle in so the top lip sits slightly above the deck stick the handle in with resin qcell mix once it's gone off glass over the top of it , sand back once hardened then make sure there are no air bubbles !
or call me I will talk you through it