I use stainless steel sheet metal screws on my rod holders, about everything including seat brackets and dab red lock tight on them in my 1648 G3 and nothing has ever come loose. Even installed a floor in it with stainless steel screws into the ribs and they hold great. Blue or red lock tite and they hold tight. Trolling motor and da ducer is also mounted that way also. Get as large a screw as possible to use.
Drill your screw holes smaller than the screws for a tight fit.