Starting with the same Forgecraft Games resin bases I used in the rest of the army I drilled a hole in the center of the base and glued a brass rod in place. I then built up a series of telescoping polystyrene tubs around the brass rod to create the armature for what comes next. The inner diameter of the inner tube was just right to mount a rare earth magnet I also mounted a matching magnet on the underside of the model.
Here is one of the bases almost completed. Turns out that as long as you are willing to go slow and let each layer dry it's actually quite easy to turn out a decent result.
Here are the completed bases with paint and texture.