If you must bond alloy sheet to fibreglass make sure you coarsely rough up the surface very well and if possible drill as many "bonding holes as feasable through the metal.If, however, you just wish to put "show" panels onto fibreglass rough up the area only you want to bond, clean with thinners and use SIKAFLEX. There are two types available, 221 being the most widely used and will support a baby elephant. If, however you do want to bond a adult elephant onto the fibreglass then use the structural grade which will quite happily take 10 tons in sheer. You will break the car before you break a Sikaflex bond!!!!!!
Regards,
GTA Racing.