molding fiberglass, hwo do u do it? Options

[DeW_H0e_GT]

ive tried molding the lip that i have (pics in profile) which was cut in half due to HK's shippign restrictions.....everytime i try to flip it over to do the bottom side it splits open!!!....

first, ive applied fiberglass resin jelly w/hardener on the front of the gap...then applied fiberglass cloth in the back with some resin to reinforce the front..BUT when i try to do the bottom of the lip its breaks on me.....ive tried it liek 4 times and its doin the same thign......ive let it sit for 4 hours and still its breakin apart everytime i try to do the bottom.....any1 know whats teh trick to doin this?.....ill upload soem pics when its brioghter outside...