I will second putting them in the fridge. They will last a little longer that way, but not a whole lot longer than the year. The latex stretches and begins to break down. Mouth calls are a disposable thing. They've got to be. Thin latex is just not made to last a long time.
Be sure to clean them before putting them away for a long period of time too. Especially at room temperature or above, bacteria can grow on them. You can end up with a 'nasty cold/sore throat' while on your hunting trip, and it can be because of that bacteria.
Vector