Ok, those of you have seen chemical damage to your covers, how long did it take? What is the inside of your cover lined with? I've been adding chlorine, and shocking while closing the cover immediately for 18 months now and my cover still looks great. The inside is lined with a white material that has a texture to it that seems to help hold the cover in place. I can see a slight color difference (whiter) where the cover is over water vs where it is over the edge of the tub. But the cover is still quite solid.
Bill believe me the damage is suttle, kind of like the brakes on your car. One day you will notice that your vinyl is discolored, dry and cracked. and the Cover has become very heavy to lift because of all the water it has absorbed and then it is too late to do anything but replace it.
If you find that statement hard to believe just use a spa blanket and watch the deterioration. With in months its color will looked bleached out and within two years you will see it disintagrate. I have seen this first hand with friends Spas who have ownership experiences of fifteen years.
Of Course I do not expect a Spa Cover to last for ever but it is not unreasonable with a little care and attention to enjoy a servicable life of Five years plus.
Regards, Zz