Open the engine hatch and locate the BIG air filter. Find the inlet pipe and stuff it if you must. I'd use galvanized wire mesh (hardware cloth) rather than steel wool (which rusts). My last coach had an inlet duct all the way to the roof, but others have an air intake in the sidewall. It's big cause diesels suck a lot of air. Ought not to be hard to find.
Former owner of 2004 American Tradition and several other RVs
Home is West Palm Beach, FL