The base was done using my usual method that I recently did a tutorial on. However, the foam by itself doesn't support a heavy metal model by itself very well so a little internal support was needed to make the model secure. I've used the plastic rulers that come with the warhammer starter boxes for various hobby uses before and they work well enough here.
I started by placing the model onto my sculpted foam and then outlined where the feet were going to sit with a sharpie and then I cut out a couple areas in the foam where I would attach two plastic supports that would secure the model to the base.
I then glued the red supports to the base. Once those were dry I glued the foam piece to the base with hot glue by sliding it over the supports and into place. I then pinned two of the raeks feet to the two red supports and glued the model into place. Any gaps between the feet and the foam were filled in using foam putty.