I have an older (late 80's) 25 HP 2 stroke Mercury on a 14'10" Johnsen. I am planning on redoing the decking and am doing my research from those that know more than I do. I currently have a 6 gallon tank, but am curious if a 3 gallon would be sufficient. Is the weight differential significant enough to make the change? Or should I just draw my decking plan around the 6 gallon?