I also added 6, four foot sections of re-bar in it also to make sure it never moves. I also originally was going to dig footers, but the husband didn't think it was necessary as the steps are hollow and not nearly the weight of the original steps. That and I got 9 inches of compacted fill underneath the concrete so I should be good.
I would have gone with the footings under the steps (just had to rebuild mine), Although mine were just sitting on an 8" slab. Hopefully yours will stay put!!