I have done quite a bit of gelcoat repair on boat hulls, decks, and interiors. If I had your issues (spiider web cracking) on the tailpiece on my bike, I don't think I would repair it with gelcoat. Perhaps if there was a very small area, then yes. But on the spider web cracks, you will need to sand most of the gelcoat down to the bottom level of the cracks, which means your fairing you will have very little gelcoat left. And then things get more complicated. As per the earlier post, it is very difficult to spray, and if you spray it, it takes a fair amount of sanding and polishing to get the gloss up. It is also much harder to colour match gelcoat than it is to colour match paint. In boats, there are reasons for regelcoating, such as scratches can be filled and sanded out. And on a boat once you start painting, you are in a cycle of repainting every 10 years or so. Not so on a bike stored inside. I would much rather regelcoat a boat than paint it. But on a motorcycle tank or tailpiece, paint is the way to go.
Stephen Hill
Victoria, BC