[Ant]

A simple way is to drill holes in the mounting face of the angle brackets, rough them up and cover with glass matt etc, so the bracket is encased in resin etc and has resin right through the holes eg 1/4" holes, and wont fall off.

Aluminium and fibreglass arent really compatible unless you do the above which is only one way, there have been some excellent tips in this post on professional products eg used in corvette manufacture. Aluminium is often used in boat building etc as a mould because fibreglass doesnt stick to it.

Another way would be to glass up some angle brackets between two pieces of alloy 90 angle space them the required thickness and then you have a bracket of the same material as a glass cobra!