I'm not optimistic the chassis brand would have anything to do with the mounts used by an RV body builder, but surely the part was originally obtained from some trucking industry vendor.
Where are these "house rubber mounts"? Could you post a picture of one? I'm no Class C or Four Winds expert, but the RV bodies I've seen under construction were welded or bolted right to the chassis rails.
Former owner of 2004 American Tradition
Home is in the Ocala Nat'l Forest near Ocala, FL