theres a special bodyfiller that bondo makes i believe thats specifically for urethane fascias. it has somewhat of a flexible composition so it doesnt crack as the fascia flexes. check your local painters supply.
Jim Hahn
1996 T-Red Contour SE Reborn 4/6/04
3.0L swap and Arizona Dyno Chip Turbo Kit
364 whp, 410 wtq @ 4,700 rpm