Unclassified to Classified HD Access

Good Day All,

Question, plan is to apply Windows Security & Critical updates to several Classified Servers (Secret) using ( a Disconnected WSUS Server).  My plan is to have an installation of WSUS on an open network (Internet) to retrieve the patches and then test/approve/scan them to export them to media (external HD) .  This media will be scanned with an AV (as mentioned) to then import them to the WSUS Server on the Secret Network.

Taking into consideration, Media Security Policies, can this external hard drive be used from an unclassified system to a secret system?

Thanks,