Eric,

I have used a polycotten outside to keep down cabin temp with great success. What you DON'T want to do is have it on there when it rains. First of all the cotton won't last long if it gets wet often and secondly, you'll have a big mess if it gets soaked.

The polycotten breathes and is soft on the paint. BTW I usually pay about $100 for a Covercraft, Poly cotton.

Good luck,