Here is the mock-up of the 5 man spider rider unit. I plan on not using the riders as it just will not look as good. The basing should allow me to remove causalities easily too.
What I plan on doing is cutting the arch just past the center keystone and then using the right half on the back of the left half. That will make the arch heavier and more stable on the base, and I'll be able to add a spider on the rear of the wall.
Careful inspection will reveal that I have already tried to position the upper spiders legs quite unsuccessfully. I'll need to cut them and green stuff the gaps to get the proper spread as the spider as the come are too narrow looking.
I also plan on putting a spider on the ground behind the poor dwarf.
One problem I have with the current dwarf miner models is that their heads are not easily positionable. I need to tilt this dudes head so that he is looking more up towards the spider on the wall and not so much looking at his feet.
Might also add one or two of the dead dwarf models stuck to the walls with spider webs (which btw, I have no idea how to model...)