We describe a theoretical proposal of a nanofibre-based trap for a Rb$_2$ molecule prepared in the metastable state $(1)^3\Sigma^+_u$. The trapping potential results from the combination of a travelling and a standing-wave fields, both carried by the fundamental guided mode HE$_{11}$ of the fibre. We show that, with an experimentally realistic choice of laser frequencies and powers, one can implement a $\approx 200$ $\mu$K-deep well at $\approx 140$ nm from the fibre surface accomodating for $\approx 500$ translational molecular states.