There are others here who are more familiar with the RP model pipeline than I am, but I will say that, to my knowledge, RP was not designed to handle contemporary IE BSDF model files.
Feel free to check out my module complexpbr, which offers IBL among other things in an easy to use package. Complexpbr -- A Module for PBR IBL, SSAO, SSR, AA, Vertex Displacement and More in Panda3D