I'll second Marks advise. Polyprop will not die from temperature cycles, but you can break it by trying to flex it when cold. Off hand, without looking up the data, I don't think you'll have any problems with cold cracks at normal freezing temperatures or a bit below. I think it's only down around 0 degrees F that cold dangers become real. Fwiw, I know several folks who winter kayak in their plastic kayaks.

I'll also second (very loudly) that UV is the killer. As is ozone. Letting the kayak set in the back yard for days on end is what will kill the plastic, making it very brittle.