You can use either material, that's up to you!
The brass wires will not be as efficient and surely more expensive.
The steel wires will be more efficient and can be found in many more levels of stiffness.
Each will shed pieces of the wire when in use. The small pieces of steel will rust and contaminate whatever they rust on, when exposed to moisture.
Using steel on a waterborne yacht is a huge No-No because the particles get on the teak wood or paint and leave rust marks, particularily around salt water. In an aluminum yacht they can even cause electrolytic deterioration to the aluminum hull.
I don't think you will have any problems using the steel around your airstream, just clean up afterwards. I have never encountered problems using steel wire wheels around my Airstreams.
And, you can always go to stainless steel, if you just have to have numerous choices.
As the Nike
logo states "Just Do It!"
technique sounds like a good one! A welders brush is a great tool to have around.