Stepside bed cross sill mounting?

[jcwren]

In the picture below, there's the cross sill (#14), and then the other two pieces shown underneath it. Are these metal or rubber?

I'm told I want to put rubber pads (like a Classic Parts #13-556) between the cross sills and the frame. LMC doesn't seem to carry the pads, and don't mention in the description what these two pieces are made of. Other companies that are selling cross sills don't indicate these two pieces.

What am I looking at here?

Thanks!