Whats the best way to attach a fiberglass wing flare to a steel wing?
I want it not to crack and split the paintwork in the future- ever!
products, techniques etc..
Appreciate your info and apologies if this has been cover before.

Never done it myself but theory is to stop any differential movement. Mount flange on inside, bolt or rivet and use Sikaflex or similar to bond as well. Once set use as little filler as possible and glass on to very clean surfaces.

I cannot see you every stopping this as the have different expansion and contraction rates, to minimise the effect you need a really good key on the metal, if you pepper the metal bonding area with little holes then the fibreglass will adhere to itself through these so be mechanically fixed.

I would use PU (Sikaflex, Tigerseal etc) as this will remain flexible. For belt and braces, laminate over the top with epoxy and glass onto a well keyed up metal surface.

what about something like this

http://www.shop3m.com/3m-automix-panel-bonding-adhesive-08115-200-ml-cartridge.html

anyone ever used it?