Hello all,

I've decided to embark on the journey of designing and making my own custom bumper out of carbon fiber.
I have alot of questions about everything, but only a few about making the plug.
I plan on using an existing bumper (injection molded plastic) and modifying it (changing some of the lines and relocating the exhaust). I want to turn this
into this

I've already purchased some Y2 Clay from Chavant, and have been experimenting with using that, but I was wondering if there were better ways to accomplish what I want to do (like expanding foam or whatever).
And if I do use the clay, what should I use to give it a acceptable finish for making a mold out of it? I've read a little about using Duratec Grey Surfacing Primer but was wondering if there are other options.

Thank you all so much in advance!