Thanks for the explanation. I suppose they are made of steel. However, aluminum can degrade to a powdery substance.
I am waiting to hear from Clifford after he sees the pictures as to get it or forget it.
The wheel hoop is the arced structure of which there are 6, (one for each wheel...)(1 inch square tube) (mandrel bent) that forms the outer arc of the wheel well, to which the aluminum siding is attached, that point being where all of the road grit and salt most often attack the bus structure thus the first places to "rust through".... where the rivets first start popping out/off...