For SteelCentral Portal, the procedure is described in the troubleshooting guide:
Switch to version 1.5.2 and download the document called:
SteelCentral Portal 1.5.2 Troubleshooting Guide
See page 38 of the troubleshooting guide.
Create a batch file and you won't have to go through this long process.. I don't know why Riverbed doesn't do it as part of the .bat file.
1. Stop authentication services
2. Stop portal web services.
3. Restart SCPortal Datastore (this step is not documented)
4. Run rpm_dashboards_backup.bat that is located in your installation directory.
As to backing up the Flow Gateway in general best practices is to not do so. In general there is no or little information stored on the Flow Gateway beyond configuration stuff (i.e. addressing, flow forwarding, etc). It is usually faster to simply re-enter the information then to restore a backup (if you consider you will need to IP the system to connect to it then all you are really doing beyond that would be flow forwarding and possibly user account configurations - of which there are usually minimal requirements on the Flow Gateway).
Having said all that I do understand there may be a desire to perform a backup (complex flow forwarding rules, etc.). Unfortunately at this time it is not possible to backup a Flow Gateway.