Rockwood06, when I get a stress crack in plastic, aluminum, or even sheet metal, I drill a small hole (1/8 or 3/16 or so) at the end of the crack, making sure that I completely cover the very end of the crack with the hole. The hole relieves the stress, and will usually prevent further "creep".
Chap , DW Joy, and Fur Baby Sango
2006 Ford F150 Super Cab 4x4
2008 Surveyor 263