Well...I simply don't have any experience with anything less than 1 layer of 4 oz. e-glass on both sides of a strip built boat. That layup should be fine for what you have described. Considering that an average size kayak might use 6 yards of cloth you'll see a savings of perhaps 12 oz. plus a few more ounces for the epoxy. Say around a pound. I suppose I would consider 4 oz. on the hull and 2 oz. on the deck...but I just can't imagine why. Point of diminishing returns...other than to say I did it. Probably total care in the construction of the boat will save you more than scrimping on the cloth. You can also not completely fill the cloth on the inside of the boat. I do this for a nonslip surface rather than to save weight but it will save an ounce or two.