I have an "extra" rear diffuser laying around and I'd like to see how difficult and time consuming it would be for me to replicate it. I doubt I can use CF, but FG should not be very difficult, right?

Any help is appreciated.

thats a big DYI your asking for, at the shop i work at we made custom fenders,hood for stillen sc,led mirrors and a 3 piece wing for the g35 coupe and to post all the steps of any piece would be huge, i suggest going to a fiberglass forum or corp site for better information...prob be your best beat

try fiberglass.com

I would say that if this is your first time working with fiberglass be prepared for a very time consuming process. It is also very messy. I know that you will have to create a mold 1st. After that I am completely clueless unless has anything to do with a custom audio system. Try to talk to Klumyzee. He should be able to walk you through the process.