I am not too worried about sunrot on my latitude (59°N). I will monitor the sails we have made from Odyssey III.
The sail of Frøken Sørensen has been in use since 2013 without a sail cover, but has been stored indoors during the previous winters. I have also taken care to secure the furled sail bundle to prevent any of the sail from flapping in the wind.
The sail for Ingeborg has only seen use for one summer yet, and it got a sail cover around Christmas. That sail cover - also from Odyssey III - was made with the un-coated side up - don’t ask me why. Anyway, if a sail cover is used between sailtrips, that should cut UV exposure with over 90%. That is why I try to make the cover super-quick to fit and remove.
If stress is the cause of Odyssey falling apart, then I have done what I can to avoid it, by doing my best to avoid flutter in the leech and by lacing the ends of the sail bundle firmly before fitting the sail cover.
Time will show - my guess is that the annual UV dose one gets in Stavanger isn’t that high.
Anyway, the Odyssey cloth was very easy to work with.
Arne