replace wood stringers with solid plastic deck molding?

[Hagman]

These are prefab stringers (and other components) that are pre-glassed, very lightweght, won't rot, and are easy easy easy to work with. http://www.preforms.com/products.php They are very reasonably priced.

Coosa Composites 1/2" 4x8' Bluewater 26 Coosa Board
$286 online