Here's another test render, this time for the defenders just outside the moon pool (You can see the surface of the water inside the dome on the left).
This render took 1 hour before I stopped it, and it looks OK with 2 figures in. Running an entire photo-story out of renders which need to be left overnight to cook is not ideal (it's why my Surgical Strike II set on Deviantart is taking so long).
I'm still not entirely happy with the crossbow, and I've realised that the bump map on the suit has the original text that I replaced with the character's name. I need to either 12 new bump maps for each name, or (more likely) remove the lettering from the bump map.
Finally, I need to find an efficient, easy method of making this look a little more like an underwater render in GIMP.
You might also have noticed that the helmet design has changed slightly: I realised that I could remove the hood model, hide part of the helmet, and increase the size of the helmet itself, so that the characters' hair could be visible underneath- which I liked the look of much better.