Intermetallic compounds R2RhIn8 are structurally related to a class of Ce-based heavy-fermion superconductors. Study of their magnetic structure and behavior is important for understanding mechanism of the unconventional heavy-fermion superconductivity. Tm2RhIn8 is unique among the series exhibiting incommensurate magnetic structure with the Néel temperature of 4.1 K. We have determined two possible sets of propagation vectors from our previous experiment on CYCLOPS. The aim of the proposed experiment is to find out correct propagation and to reveal ground state magnetic structure of Tm2RhIn8.