My PVC panels would have lasted better had I not piled them up on a warm day in Spring. I can't recall now why I didn't put them away properly but I took them off in a rush because the weather suddenly got warm.
When I went back a couple of days later to stack them properly, those in the middle of the pile had distorted with the heat from the Sun.
I managed to put up the distorted ones on the lee side, with inevitable gaps, but they snapped if I tried too hard to re-shape them. They'd only done one winter and the damage was all from the sunshine.