~ I own a pair of CLC Chesapeake 16's (also a full volume expedition sized boat) and occasionally have similar issues. I built mine with a retractable skeg and that corrects the problem very well. Weight is a factor as these boats do handle better with a significant load. I don't think adding a gallon of water will be enough though as that will only add about 10lbs of weight. My wife and I frequently will paddle with 100lbs of weight and still the deck will still sit two inches above the water. CLC sells a retractable skeg kit that might fit your boat if you elect to go that route.