Instead of using the standard models for Crypt Ghouls, I decided to use Forest Goblin Spider Rider models.
While I liked the look of spiders, the hardest challenge was figuring out how to fit the models on 20mm square bases. The solutions I used involved trees and branches from the Citadel Woods, and using larger 40mm square bases, which counted as a group of four spiders each.
All of the spiders had areas that had to be covered with greenstuff. The most obvious place was the hole which the Goblin Rider would sit. There was another hole was on the the spider's belly and a gap in the abdomen.
They still need some adjustments, mostly angling the spiders and perhaps repositioning some of the legs. Most spiders are not glued down, simply pinned to the trees, this lets me remove them if I want to. It will make it easier to paint them.
I am still trying to think of a good paint scheme, all that I know is that I will probably use some kind of brown color scheme.