  Supernova (SN) 2008bk is a well observed low-luminosity Type II event
visually associated with a low-mass red-supergiant progenitor. To model SN
2008bk, we evolve a 12Msun star from the main sequence until core collapse,
when it has a total mass of 9.88Msun, a He-core mass of 3.22Msun, and a radius
of 502Rsun. We then artificially trigger an explosion that produces 8.29Msun of
ejecta with a total energy of 2.5x10^50erg and ~0.009Msun of 56Ni. We model the
subsequent evolution of the ejecta with non-Local-Thermodynamic-Equilibrium
time-dependent radiative transfer. Although somewhat too luminous and
energetic, this model reproduces satisfactorily the multi-band light curves and
multi-epoch spectra of SN 2008bk, confirming the suitability of a low-mass
massive star progenitor. As in other low-luminosity SNe II, the structured
Halpha profile at the end of the plateau phase is probably caused by BaII
6496.9A rather than asphericity. We discuss the sensitivity of our results to
changes in progenitor radius and mass, as well as chemical mixing. A 15%
increase in progenitor radius causes a 15% increase in luminosity and a 0.2mag
V-band brightening of the plateau but leaves its length unaffected. An increase
in ejecta mass by 10% lengthens the plateau by ~10d. Chemical mixing introduces
slight changes to the bolometric light curve, limited to the end of the
plateau, but has a large impact on colours and spectra at nebular times.
