Brass is pretty stable so using steel should not be an issue, just be careful not to strip it out as brass is softer then steel, looking up torque specs would be a good idea because if a connection like that comes loose it will melt the connection, I bought a bag of bronze lock washers from McMaster Carr along with brass washers and bronze bolts, but you shouldn't need to go that far.
Using some copper or silver, electrical grade never seize can be a good idea as well or a good dab of dielectric grease, it will keep moisture out.
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