I would like to create an invisible skybox and I wonder if it is possible.
What do you mean by invisible ?
You could just make a custom skybox with 6 white texture. So you have a totally white skybox.
Invisible skybox doesnt really make sense, as your map skybox brushes need to display something.
looks fine to me
what I want to do is hide the skybox because the real skybox is a prop.
If the skybox is a prop that covers a 360 degree view, then just make a normal skybox with the skybox texture.
Use 2dskybox texture instead of toolsskybox