I have always done the same thing that Mike does.
Some of the waxes have silicone in them, so I try not to use those on surfaces that will come in contact with materials that will be finished.
But that is of no concern for your grinder.
The T-9 Boeshield is great stuff. Seems like just about any wax placed over it will go a long way towards warding off rust.
Try not to get too wrapped up in which wax you use, unless you're faced with the situation I described above (e.g., table saw and jointer tables, etc.).
Johnson's paste wax, Renwax, I've even used the various "automotive" waxes to great effect.
I don't know if it's the Boeshield, the wax, or the combination of the two that provides the protection; all I know is that it works well.
Short of powdercoating or painting, whatever method you use will require reapplication on a periodic basis.