Any tips for how I should go about best fixing this?



I got fiberglass mats and such but I am a novice with their usage and I don't know anyone thats good at working with it. My plan is to simply build it up layer by layer and until it has the proper shape, more or less, and then sand it down.

 

Now I don't know much about working with fiberglass, my dad has mats and whatever you call the goo in english (not my first language) that I can use but I am not sure about how to go about getting the proper shape here. I am wondering if there's some kind of putty or something I can use to make a mold or something out of?

I was thinking you could put such a putty in there where the missing bit is and shape it properly, then remove and put a mat on it and let it harden, then remove the putty and put the mat back in use it as a base to keep layering up. The base would have to be smaller than the rest of the surrounding area ofcourse to allow you to build up several layers.

Thats the idea I have in my head anyway.