Cannot apply texture on each side of a triangular tube

Maybe Im missing something obvious but I cannot figure out how to texture each side with different materials of a in my case a triangular tube. I tried techniques using texture3d together with material and texture SOP but I guess I need a way to get my uv-coordinates right?
This wouldnt have been any problem if it was a box using a cube-map but I run into problems with my three-sided geometry.

I anyone has got an example it would be very much apreciated.

texture_triangular_tube.tox (8.3 KB)