Select the project timeline that you want to backup in the Project Window
Go to >File>Project Manager
Choose the sequence you want to backup
Copy Files to a New Location
Browse to the location you want to back the files up to
Make a New folder on the hard drive so it is more organized
Select the folder and click on "Choose"
You can click on Calculate to tell you how much disk space the backup will need.
Save the project by clicking Yes here
Project Manager will start copy/backup process
To test the backup unmount all the original drives except the one with the backup on it and open the premiere project to make sure it worked.