First of all thank you all very much for the great posts! They were really helpful!
After reading all of the information found here though I had a hard time figuring out how to properly get the cube texture into Unreal. Following the documentation was hard as it was lacking information. So for all of you looking for a way to get custom skybox in Unreal. This is the way I did it.
-Take an image you want to use as a skybox and cut it into 6 images using free software like cubetheSphere
-Following the UDK tutorial found here place your six images in order and rotate them correctly. (https://docs.unrealengine.com/latest/INT/Engine/Content/Types/Textures/Cubemaps/CreatingCubemaps/index.html)This was the hardest part for me as I didnt know which picture (top, bottom, front, back, right, left) corresponded to which number. Here attached is an image showing the proper order.
-Export the image in the dss. format out of Photoshop using the Nvidia plugin https://developer.nvidia.com/nvidia-texture-tools-adobe-photoshop using the options described in the Unreal documentation ( https://docs.unrealengine.com/latest/INT/Engine/Content/Types/Textures/Cubemaps/CubemapTools/index.html
-Import the image in Unreal. You have to change some options for the texture here as well. I followed this tutorial. https://wiki.unrealengine.com/Skybox_from_DDS_cubemap
-Verify if the texture is rotated correctly. You can do this by writing the numbers in the photoshop document and rotating them along as the images. The numbers should be matching as shown in the unreal documention. For some reason I had to rotate number 6(bottom) 180 degrees.
-Create a skysphere. I used the existing blueprint skysphere to replace the existing one.
-Follow the same tutorial https://wiki.unrealengine.com/Skybox_from_DDS_cubemap
to create the material to use for the skybox. It contains an unlit material,constant3Vector, reflection vector, and texturesamplecubemap nodes plugged in emissive. Your new texture goes in the texturesamplecubemap. It will be in linear color. You can preview how the skybox looks like if you right click preview node. At this point it should be showing the skybox. If its not your texture may not have been imported correctly.
-If your skybox is too bright add a multiply node with a constant3vector to change its brightness.
That’s it. Hope it can be helpful to someone 