Find styrofoam the same thickness as the ribs in boat . Use that under flooring that allows you to go thinner on aluminum . adds support, insulation from cold water, and some sound deadening . I personally wouldn’t use any thicker than .125 gauge . You’ll find the 1/4 is going to be extremely difficult to deal with . And way overkill.
Thank you. I bought a blade today and if the weather cooperates I will make some cuts tomorrow. This site is great.