The welds on aluminum tanks are prone to leak when the tanks are filled with diesel fuel.I have a 250 gallon aluminum tank on the bed of my F550. No baffles. The rear axle is rated to carry 17,500 lbs but I can feel the diesel sloshing around in there if its half full. I would not want a tank of any decent size on a boat that was not baffled. Free surface affect and all
I know of a few boats where the tank let go. I think the modern plastic tanks are the way to go.
Very Best Robin