I have had this problem and the ONLY thing that has been able to withstand the direct sunlight from the west is a product from Holland that they use on boats called "Epifanes"
http://www.jamestowndistributors.com...duct.do?pid=92
It is expensive but worth the money. You can order it from Jamestown Distributors or amazon. It has the most solids. It does take about 8 coats.
PM me any time and I will call you to discuss if you want.
Duckaholic