bungee cords

I've have side saddle bags, but have been securing a bag on the passenger seat with bungee cords. I've been attaching one end of cord to the base of the rear turn signals and the front to the top base of the shock absorbers (diagonally across the bag). The end with the shocks seems pretty bullet proof, but the turn signals are plastic. Even though I secure the cord to the base and it seems very secure, am I asking for trouble there? Where else on this bike could I secure them?

Thanks,

Keith