Matt O'Toole wrote:
20 extra gallons is not a big deal. Get a few jerry cans and tie them
down safely. For a more permanent solution, add a tank. With a
relatively common, mainstream boat you should have no trouble finding a
ready-made plastic tank that will fit somewhere.

Matt O.

That's what I did on my old Chriscraft Cavalier '27 when I cruised down
the Illinois river from Peoria to Alton. We strapped 6 jerry cans
(back when they were made of metal) onto the dive platform. I knew we
wouldn't need them going down, but coming up , yeah, we tapped into
them.