[master66]

that's a heck of a chunk missing! So the only real way to effectively fix cracks "and have them last" is to grind into the crack a little ways down about an 1/8th inch, this will, one clean out the crack and two create a trough effect to house the fiberglass filler or a two part epoxy glue that will bond to bare fiberglass . You can also do this on the back side to make sure you are getting a good bond. I will also if possible try to pull the crack apart a bit to see if I can get some filler or epoxy in the crack . Just remember to keep the fiberglass trough lower than the surface because you will have to put body filler over it.