To make the fibreglass cowl, I first made a plug with the exact shape of the actual cowl.I did this by slicing the CAD model and printing out each slice.

I then cut them out from wood and made a wood/PU-foam sandwich. PU foam is poly-urethane foam. It is similar to the green foam you can get from the florist, except it is much firmer. It can be cut and sanded without worrying about poking a finger through it.

The wood/PU-foam sandwich was then sanded to shape. Any holes and bumps were then filled out and the plug was sanded again. This filling/sanding work continued until it was the right shape and completely smooth. The picture shows the plug after its first sanding/filling cycle.

The plug was then spray painted with an automotive primer. This made the plug real smooth, making any tiny imperfections visible. Filling and sanding was necessary once again.