  We analyse Chandra X-ray Observatory observations of a set of galaxy clusters
selected by the South Pole Telescope using a new publicly-available
forward-modelling projection code, MBProj2, assuming hydrostatic equilibrium.
By fitting a powerlaw plus constant entropy model we find no evidence for a
central entropy floor in the lowest-entropy systems. A model of the underlying
central entropy distribution shows a narrow peak close to zero entropy which
accounts for 60 per cent of the systems, and a second broader peak around 130
keV cm^2. We look for evolution over the 0.28 to 1.2 redshift range of the
sample in density, pressure, entropy and cooling time at 0.015 R_500 and at 10
kpc radius. By modelling the evolution of the central quantities with a simple
model, we find no evidence for a non-zero slope with redshift. In addition, a
non-parametric sliding median shows no significant change. The fraction of
cool-core clusters with central cooling times below 2 Gyr is consistent above
and below z=0.6 (~30-40 per cent). Both by comparing the median thermodynamic
profiles, centrally biased towards cool cores, in two redshift bins, and by
modelling the evolution of the unbiased average profile as a function of
redshift, we find no significant evolution beyond self-similar scaling in any
of our examined quantities. Our average modelled radial density, entropy and
cooling-time profiles appear as powerlaws with breaks around 0.2 R_500. The
dispersion in these quantities rises inwards of this radius to around 0.4 dex,
although some of this scatter can be fit by a bimodal model.
