Auto body repair & detailing: primer bubbling on fiberglass, gmc stepside, stepside truck

Question
i have a gmc stepside truck with fiberglass sides. the paint started peeling off shotly after i purchased it. i removed all the paint and primed it with high build primer. 2 weeks after i primed it the primer started to bubble. what should i have done to prevent this.  sealers or another primer ok .need help  

Answer
Sand off all your primer to bare fiberglass once again with 320 grit sand paper. Then wipe down the parts with a final wash paint prep cleaner. Then use a sealer, apply three coats and let dry then sand with 400 grit sand paper and apply the high build primer, two coats and let dry.
       Thank you for the question !
       Ken