Re: cold weather and PVC tubes
Yes. When there is ice covering the water!
No, seriously though, you may want to contact Zodiac and ask them. In my experience, I've used my C3 in freezing temps with no ill effects. Keep in mind though, that in very cold temps, the boat may feel like it isn't up to pressure (feel "spongy"). Also, the water temp is usually a bit warmer than the ambient air temperature.
You DO NOT want to unfold or fold a cold pvc boat. If it is folded, bring it in and let it warm up before unfolding.
Btw, what kind of cold temps are you talking about?