For the weather Wyatt and I get in the Northeast, I am not going to let my Nacra sit outside in the winter. Waking up to 1/2 inch of ice on everything would break my heart. I have found indoor space for it in a neighbors barn. I think it's worth it to get it out of the UV alone.
If you are going to go with the tarp idea I would purchase again the material (Yard Softouch By Odyssey)I got from www.rochfordsupply.com. It has a soft side and a durable vinyl-like side and made great cheap covers for my hulls to transport cross country with no damage.

Good luck,
Greg

The nice part about being a pessimist is that you are constantly being either proven right or pleasantly surprised. - George Will
"It's not that liberals aren't smart, it's just that so much of what they know isn't so" -Ronald Reagan