NewRiverSmallie

Greetings all. Long time lurker, first time poster. I have a 14' Lowe "Lake Jon" and I want to mount pedestal seats to the factory bench seats. I believe that the aluminum on the bench seats is too thin to support a pedestal (I weigh about 230 lbs), so I'm mounting the pedestal base to a 3/4" thick piece of treated plywood which I have carpeted. I will then mount the plywood to the boat's bench seat in order to better distribute the stress. My quesion for those of you who have done something similar, is what kind of screws would be best for mounting the plywood to the bench seats? I don't have access to the underside, so bolts/nuts/washers are out of the question. Thanks for any replies!