Need advice with paint

Hi

Can anyone help me with advice on painting my hood scoop ? I have a twin snorkel hood scoop on my 75 duster, I think it's fiberglass, anyway I just got a killer paint job on my Duster and the paint on the hoodscoop keeps bubbling up. I have cleaned and reprimed it and painted it three times now and it still bubbles up after a couple of weeks. Whats the deal? I am not a paint & body man (dont have the talent for that) but willing to try whatever it takes. Thanks for any & all advice .