We vault Mon-Sat.
Offsite catalog tape is created via the vaultrun session/profile using a dedicated pool and tape range(10 tapes, 7 day retention). Then we do a Mon-sat onsite catalog copy in the afternoon via bpdbbackup command and AT, utilizing the alternate media in the catalog backup setup.
You need to define your requirements, then select what works for you and gives you the best recoverability. The above method works for us, it may not for you. But you're on the right track, you need those catalog backups for recovery.
This line is your question I find a little confusing,
"Using Vault I'm going to Dup the Tapes."
You do know you can create a catalog tape from the vaultrun? No need to dupe.