Boat is a 1981 14' Mirrocraft with original factory foamed bench seats. Have 2-Millenium seats mounted on 7" bar stool type swivels. I used SS sheet metal screws and need to tighten them every year. I've never liked that procedure and I'm looking for something more permanent. I remember a guy using high shear rivets. Not sure I could do that, looks like the back needs to be backed and I don't have access under the seats. Would 1/4" aluminum rivets be better than sheet metal screws?