I have seen here on more than a few occasions when someone would ask the best way to glue one thing to another. I heard about this website on a podcast, so give this a try next time you have this question.
Fibre (in the original french):unsure glass to fibre glass: i would go for more of the same, in some cases cleaning the crack :lol or break and more chop strand (chop it up and plug the hole etc) or matting and resin if applicable, (like a surf board repair) that is to say if the bond needn't be invisible, to a degree one may sand back to disguise the repair but dont go too far as you may sand right back to the original break.
Otherwise UFO industrial superglue for a bond (and the accelerator spray too just don't breath that M.E.K and after, vehicle BOG to fill and sand..
When i say vehicle BOG i keep in mind that you guys call a TOMATO different so i will be explicit:
Vehicle bog used for panel repair on motor vehicles is an A+B mix catalytic putty which may be sanded and prepared to a smooth finish.
3m make the best bog, its called gold medal or something like that and its worth the extra $$ it is easier to work and provides a gorgeous satin consistency for sanding and finishing. (provided you nail the A+B proportions)
Keep in mind the bog is to hide the bond cosmetically not provide it, and no bond will work as well as fibre and resin on fibreglass.
The other product I used alot on sets and props was ADOS F3 and F4, made by CRC (New Zealand's answer to WD-40) these are a brown contact adhesive and the different numbers denote the viscosity (from memory i think the F4 was less runny and really good for situations on under-hangs and situations fighting gravity as it cures. :thumbsup
The cardinal rule if you are gluing, like painting is sand and prep, you will provide a far better microscopic surface for the glues to bond with a little prep work.
And really the best prepper in the world is the 3M green pan scrubber as it keys the surface and doesn't scour as long as you're gentle (if you prep with water even kinder to the surface again)
We used 3M pan scrubber on stainless and aluminium welding jobs as a finisher too it is magic stuff.:love
Also if your new to a product do try a glue test piece to check if it will deliver your expectation (even in the workshop surrounded by veterans we tested products when needed) to avoid disappointment.:cry
hope this helps.