RF600VPN or RF660VPN behind a NAT box doing IPSec Pass-Through in Manual Mode to another RF600VPN or RF660VPN.

See example 5 in the RF550VPN - RF560VPN - RF600VPN - RF660VPN Reference Guide [Rev. x - Tunnel Examples in Manual Mode - S000308x]. Download it at:

http://www.multitech.com/en_US/DOCUMENTS/Families/RouteFinder_SOHO/manuals