The methods outlined in Easy Composites tutorial videos are really the most straight forward way to tackle a job like this, so I'd suggest starting there. The pattern making tutorial is very relevant, and then the split mould tutorial is likely to cover the techniques and materials for making the mould. Not sure if you have ant CAD experience, but if not then getting someone to fab something up out of metal may be the quickest and most accurate to tackle the pattern.

As for the fixings, there's a few options really, BigHead fasteners, nutserts, nut plates, etc etc. Depends on your design and what will work.

Hey, I'm new here but have always loved cars. This project will be for an Audi S4. For our car platform however, the intake options are less than ideal - otherwise I would buy one. 

An expensive but poor design:


This intake design is ideal, but it isn't for our car and serves as the inspiration for the project:


That said, my idea is to construct a snorkel that could work in conjunction with one of the heat shield only designs as such below:



Now, while I have never done any projects like this - I am pretty handy and learn quickly. I am looking to make a permanent mould, so that it can be replicated... but I have to design the shape first. I'm sure more questions will arise, but the two that I can think of are:
1. What is the best method to create an accurate mould?
2. If I make it a two piece that surrounds the filter, how do I set the threads for the screws to bolt down the lid? (See below for example):



Thank you SO MUCH in advance!!!