Working with Textures, Models, and 2D - Mastering Unity Scripting - page 292

To this end, change the Depth value of the new camera to any value less than the
depth of the first-person camera; such as -1 . Remove any audio listener components
where required.
Creating a second camera for Skybox rendering
Assign a unique Skybox texture to each cube face and take care to align them
seamlessly by rotating or adjusting the Quad alignment as needed. Then, change the
material Shader type for the Skybox textures to Unlit/Texture , making the Skybox
immune to scene lighting. The Skybox mesh should start taking shape, as shown here:
Adding Skybox textures to the Quads