Thanks zlyricist,
The rear of the enclosure is fibreglass, using the car as the mould as shown here. Fark I hate that stuff!
The rest of it is wood and a little bit of foam filler to get the contours.
Here you can also see the braces inside. I just kept tapping on the fibreglass to find the areas that needed them.
To finish I give it a hit with some spray putty to get rid of some of the imperfections.
And it's all covered with the same vinyl that I used on the doors.
I might go back and recover the enclosure after going over it with some body filler. Just to get the contours smoother.