Unreal lets you create an entire sub-level which can be used as a skybox. More than just background bitmap(s), you can put anything in there. I'm looking for more than just atmospherics and day/night cycles. I'm looking to put in things like airplanes and meteors and such. Also Unreal lets you position the camera within that sub-scene, can that be done? I'm guessing it would be like RenderToTexture but on 6 textures of a skybox. Like setup up the subscene (in a different layer), with 6 cameras pointing out in cube-style, render each to a texture, and use those RT's as the skybox of the main scene. Is that even possible?
See this topic. Basically you use two cameras, no rendertextures needed.
Unity FPS Source/Unreal engine style skybox! C# - YouTube I made a video on this!