I added three knees on each side as well as the glass. I wouldn't rely on just the couple layers of glass to add stiffness

To clarify my earlier comment: more glass on the hull will do one thing well. It will greatly increase the impact resistance. My 20MA and 25 both have some cracking from what looks like bouncing against a float, or coming in a bit inelegantly to the gas dock. It also will help with encounters with the bottom, which can happen when you are fishing or beaching. It isn't super efficient at increasing hull stiffness in the same way as tying together a box structure is, but it keeps the water out of the hull.