Dahlias do get better in second year and prob in third year as tubers are much bigger etc. Some dahlias are so vigorous that they occupy more space than I would like them to so I split these every year or two. As others have said cold wet conditions are fatal to dahlias and as long as the tubers are full and fat I wouldn't worry about them drying,out over winter. Fleece, paper, vermiculite, cardboard boxes, dry mpc anything that will protect from frost and keep them dry. Most of mine that are lifted..keep many in the ground.....are potted up using dry mpc and fleeced if very cold conditions are forecast. In spring a light spray of water and the,cycle begins again. In the ground mine are later to show signs of growth but soon catch up