I'm back again (told you I was making a lot of progress!) and this time it is the carapace that is finished.
You can see here, the torso ceiling section that fits into the carapace, that I finished earlier in the project.
Build-wise, the carapace wasn't that tricky; I had to trim down one of the sides that sits against the torso, due to one of the torso sections not being entirely straight - but the part is not visible when assembled. I also added the hatches to the carapace that fit over the side compartments of the torso - meaning that those interiors are now visible. They were a little awkward to add to ensure that they were flush to the torso, but also had a strong join on the carapace - in the end I had to greenstuff a few gaps where they meet the carapace, but they look seamless now from the exterior.