  We use Modules for Experiments in Stellar Astrophysics (MESA) to construct
stellar evolution models that reach a hydrogen-deficient, carbon-rich giant
phase like the R Coronae Borealis (R CrB) stars. These models use opacities
from OPAL and AESOPUS that cover the conditions in the cool, H-deficient,
CNO-enhanced envelopes of these stars. We compare models that begin from
homogeneous He stars with models constructed to reproduce the remnant structure
shortly after the merger of a He and a CO white dwarf (WD). We emphasize that
models originating from merger scenarios have a thermal reconfiguration phase
that can last up to $\approx$ 1 kyr post merger, suggesting some galactic
objects should be in this phase. We illustrate the important role of mass loss
in setting the lifetimes of the R CrB stars. Using AGB-like mass loss
prescriptions, models with CO WD primaries $\lesssim 0.7\,M_\odot$ typically
leave the R CrB phase with total masses $\approx 0.6-0.7\,M_\odot$, roughly
independent of their total mass immediately post-merger. This implies that the
descendants of the R CrB stars may have a relatively narrow range in mass and
luminosity as extreme He stars and a relatively narrow range in mass as single
WDs.
