How can you protect your vinyl boat seats from UV?

Some Vinyl conditioners have UV protection now, you may want to try products made for spa covers ( cheapest, or perhaps one made for marine purposes like

Boat Bling, Inc CS0032 Condition Sauce Interior Cleaner & UV Protectant

I recently bought a pontoon boat and it did not come with a cover. All the local upholstery shops are 2 months out for being able to build me a cover. The seats are in good condition now and I want to keep them that way. What can I do to protect them from UV breakdown in the short term? I know UV issues are a long term exposure issue but 2 months in the hot summer still isn't great. I'm thinking about covering them with bed sheets to keep the sun off but I'm concerned this will cause mildew/mold.

Thanks for the help!