1996 Saturn SC1 Body damage, what type of bondo do i use??

i have a saturn with a hole on the right rear, beneath the taillight. someone has tried to repair it themselves and did a horrible job. please help me to no make the same mistake. it looks like they used some time of fiberglass and resin to patch it up last time and it peeled of at one side. i am not sure what type of filler to use on it. can i use the basic bondo or does it need a fiberglass bondo, maybe i cant even use a bondo? please help. thanks. Roy Shamblen