I am replacing some rotten window sills. (These are the exterior sills, not the interior ones, AKA stools.) I have already removed one (à la the Tom Silva video) and am having the wood for the replacement sills milled from its profile. I plan to cut the side-horns (or whatever you call them) on the replacements as I remove the old sills. I will then prime them all over, especially the end grain, and will caulk appropriately.
My question has to do with attaching them. Must I use nails? I don't have a nailer and really don't want to spend the bucks on one right now. Wouldn't screws work just as well? They would certainly make life easier for the next owner to replace these sills a hundred years from now.
Any other helpful hints?