Create a new database the same way you created the existing database.

You should keep the RMAN database in a different machine altogether. So in case the PROD machine goes down you still have the RMAN to recover your DB. If they are on the same machine then if machine goes down your DB as well as the RMAN goes down.

In the 5th step after creating the catalog connect to remote target database and then register.

RMAN> connect target sys/[email protected] catalog rman/rman@rcat
RMAN> register database.

For more details Read

http://download-west.oracle.com/docs...a76990/toc.htm

HTH