Sorry for double-posting
@TheJamsh
I found some interesting examples of portal rendering. It’s not in Unreal Engine but in theory it should be the same I guess.
OpenGL Portals: OpenGL Programming/Mini-Portal - Wikibooks, open books for an open world (Source included on the bottom)
Unity3D Portals: Unity 3D - Portal Room Cubes via Stencil Buffer - YouTube (source code: http://www.noisecrime.com/unity/packages/PortalRoomCubeViaStencilsExample_u4.2.zip)
Both are using stencil buffers to achieve the effect.
Now it would be good to know how to integrate this into Unreal.
Btw… I’ve tested your Epic Mega Game Jam entry, but unfortunately the portal rendering was not visible 
Other than that it was awesome! respect!
I would be so grateful if you could help me out with this.