We ran the Workbench article a while ago showing how these figures were painted up – now, here they are based and ready for gaming.
The base is a round steel disk. Spackle was used to smooth the miniatures' bases into the steel disk. The base was then painted black. Glue was brushed onto the dried base, and the bases were dipped into a bowl of black art sand. Finally, matt spray was used to help secure the sand in place.
Horror figures may need to be used in both indoor and outdoor environments. These gray bases work for me either way.