tail light fillers

Im wanting to shave my tails on my corolla and debating between fiberglass and metal. I want to do metal but dont currently have access to the tools to get the right shape to make the fillers and nobody will make um. Whats yalls opinion on fiberglass fillers?

with the weather of the metal shrinking and expanding it will crack the fiberglass so i wouldn't do it

alright appreciate the input