Ok, I found out that the skybox thing was the culprit so I can't use images for north, south and so on.
Another thing that I just can't get to work is when I export my 3d models from blender with its mtl file and showing correctly with my image texture in blender. I don't see the texture on my model in RPG Maker.
So my question would be, how do I get my image texture to show on my 3D models in RPG Maker as well?