I had decent luck getting it to stick together with the "epoxy for plastics" at home depot. and found one of the UV sika flex with an activator sticks to it well but I cant recall the numbers right now.
Not sure on the fiberglass part but I glued thin strips of Starboard to the bottom of my alum fuel tanks to keep an air space under them. 5200 was the recommend adhesive and it appears to have worked just fine.
Try one of the plastic-welder epoxies at the hardware store. the trick is to get one that contains "methyl-methacrylate" as not all plastic welders do. this is very similar to plexus and will create a chemical bond with the starboard. This is what I use to repair my Smart-rails at the suggestion of the manufacturer.