Is your steel steerer 1-1/8" as I presume the stem clamp is?
I have an FSA stem with the same "open back" design but it's installed on a 1" steel steerer so the exposed steerer is covered by the aluminum reducer bushing.
If you don't need the bushing, I'd just paint the steerer to protect it. If you paint it black, everyone will think you have a carbon steerer.
