hey joel, i used 14ga aluminum for both seats, it tends not to ripple as much when hammering and is easier to smooth and sand without burning through, could use thinner, but i'm not racing these things so it didn't matter too much to me. p.s. if you have a bike on the road, hit me up sometime, last weekend i took the 400f out with some sport riders and went waaay too fast out in the finger lakes :-D