Mdo
Here in Southern South Carolina we haven't been having any problems with MDO. I use an exterior Sherwin Williams primer and Sherwin Williams exterior paints on it. I have only been in the business for 5 years, but haven't seen a problem with it yet. Like anything else, if you don't prep it right and take care of it, mother nature will only destroy it.
GP have you tried Alumapanel? They carry MDO in as many ways as I can think of i.e. Good 2 sides, primed one side or 2, gloss finish one side or 2, and etc.