From:
http://englishrussia.com/?p=1949
For anyone considering DIY aero mods, you're going to love the DIY, low-tech method this guy used to goop up and sculpt an entirely new body on a Mercedes coupe using polyurethane foam.
Not apparently for aero, but the low-tech construction techniques should provide inspiration:
Many more pics:
http://englishrussia.com/?p=1949