Philon exterior Yellowing?

Is there any thing that can be done to minimize the yellowing effect to the philon siding on my 1996 Ford Jayco Eagle MH. I sure it can't be returned to original state but can anything be done to prevent it from worsening?
Philon exterior Yellowing?

The best way to keep it from yellowing is to wash and wax it on a regular basis. Once it has turned yellow, washing and waxing is also the best way to keep it from getting worse. I don't think there is a product out there that can reverse it. Also try parking at different angles to the sun instead of the same way everytime to keep the sun from constatly beating on the same side and at the same angle day after day.