Good question FishHawk. I'm wondering about my Yak being strapped to the car roof for a day if I decide to 'whimp out' and jump the rip ryder.
I seem to remember reading somewhere that the modern plastics (linear polypropylene (sp?)) are more resistant to UV than earlier materials. Long time since I did any Organic Chemistry but UV effects are cumulative over time.
Went to the WS website and they recommend 303 UV protectant. Lots of places to get it - here's one: