I asked CC the question. Here's their reply:

Mr. Faulkenberry, if possible, indoor storage is the best for the actual pontoons & bladders, leaving them in the garage or a shed is an invitation for rodents to make a nice cozy home for the winter. Anytime you can avoid excessive 'folding' or 'creasing' of the bladders the better, ideally, if you remove the pontoons from the frame and store them flat folded in 1/3's in a temperature controlled environment, (making sure that they are absolutely dry inside and out), you should be fine. It's when they are left outside in very cold weather that the PVC bladder material can become 'brittle' and susceptible to mold & mildew, hope this helps, Thank You. The Creek Company