If you guys recall the old 1980-1983 Toyota SR5 4.4 trucks they had the rear fender wells painted and they were a very flexible fender piece, When Imron paint came out so did the Flex Additive product and they never cracked and they were super flexy and then some.
Talk to Lanzini Painting in Huntington Beach and ask him what he thinks, Hes a cool guy, you will find him and his work on Fooses show, overhaulin.
http://www.lanzinibodyworks.com/