I was originally thinking about getting an auto trimmer to do it but I called a couple of places, dropped in to see one and the prices were more than I wanted to spend so I was thinking of doing it myself.
I've done some research (this thread provided some inspiration http://www.mgexp.com/phorum/read.php?1,1624878) and it seems like the DIY'ers who do van conversions, custom interior trims and custom sub boxes seem to use unbacked carpet like this http://www.daleys.com.au/products/view/209 which has some stretch, liner to blunt things like bolts and contact adhesive to stick it down.
Obviously it's a bit of work in mocking it up, cutting and then fitting.. has anyone done anything like this before? Any tips or advice?
Where I'd be carpeting:

