Render Settings

Setting up a V-Ray raw image file in RPManager is pretty easy actually. First, you need to uncheck "Save File" in Common Params after that, you need to activate "Auto Raw Path" which can be found in "Output" -> "Open Vray Cache/Raw Manager". Select the file extension "Ext:" you need your renders to be saved in and click close. After that go to "Render Setup" and make sure "Enable built-in frame buffer" and "Render to V-Ray raw image file" are checked (keep in mind that you need to uncheck "Render to V-Ray raw image file" if your doing some test renders or your renders will be overwritten).

What is "Output Preferences" in RPManager? 

Each pass you setup in RPM is typically intended to be rendered at some stage, and this requires that a unique output path or name is set for each pass. This is done by setting up Output Preferences.