Several months ago I fitted the fiberglass roof panel to the steel body and yesterday I decided to bond the panel in place using a 3M panel adhesive. Using a wire wheel in the angle grinder I removed the paint on the steel roof and cleaned the surface really well using a quick evaporating non-residue thinner. I sanded and cleaned the edges of the fiberglass roof panel before applying adhesive.
The front edge of the roof panel has a very narrow contact surface so I wanted to make sure there was a good bond between the steel and the roof panel. I applied the adhesive to the steel roof and spread it out to cover all the bare metal surfaces. I applied a bead of adhesive on the front inside edge of the fiberglass panel so that it would run down to form a good bond on the inside between the fiberglass and steel. I used weights to hold the roof panel tightly against the steel body and let it dry overnight.
It feels really solid and there is very little excess adhesive that I need to remove. I’m going to use the wire wheel to remove the rest of the red paint on the factory steel roof structure. I’ll use body filler to fill some small gaps on both side of the roof panel then apply a white primer.
I added small support braces ahead of the rear wheels to locate the bottom edge of the rear quarter panel. They are strong enough not to bend if I high center the car or bump a curb. I made the supports short so that I can slip a rod into the end and lock it with a bolt. The rod will complete the distance to the quarter panel and allow some adjustment.
My Stradale 
Excellent ive done a similar thing using panel bond, should be much better this way less leaks and noise 🙂
I was a little skeptical of just gluing panels in place with no mechanical fasteners but this adhesive seems really strong. On the bottom edge of the fiberglass door skin, under the boxy section, I welded a few 90 degree brackets to the metal door so that the adhesive would have more contact surface but it probably wasn’t necessary.