Hey,
Really nice tutorial you made there. 
Used it in a project and got it to work pretty fast.
The only problem i encountered is that when you package the project the Portals don’t work any more and i didn’t find anything about that in the thread or in tutorials. 
First i thought the problem was in my implementation, but when i try packaging your example project, it produces the same bug.
Any idea why that may be happening and how i could try to fix it?
Edit: I didn’t really explain what i mean properly i now notice. 
And the Problem also occurs in Standalone mode. The portals show the wrong material and the console doesn’t show errors. It shows only the beige kind of material you see in the browser.
Edit2: Actually found the fix myself, so posting it here to maybe help someone encountering it too. @redbox Maybe it is of help to you too.
In the BP_BaseRenderSurface class, in the function InitSceneCapture you get the Viewport size as a Vector2D. But when the project is packaged or in standalone mode, this function returns 0 because it is executed before the HUD is even registered to the Viewport.
First of all i changed the function to reference the owning player controller to always get the correct viewport and secondly i made the class delay 0.5 seconds before initializing to make sure the Viewport ist registered correctly. Then everything works perfectly.
Hope this helps someone as it was a pretty big pain to find, but i am also pretty new to Unreal and find debugging packaged and standalone pretty tedious. 