Sorry for the delay in updating this, other bits of work got in the way as ever...
I've finally tried this script out entirely offline and have removed the zenoss-deps and the epel install sections entirely and it proceeds ok and installs a working Zenoss instance. Success! Thanks!
Commented out lines as shown below starting from around line 158
# JC - get the zenoss deps (which sorts the rpmforge requirement)
#wget --no-check-certificate http://deps.zenoss.com/yum/zenossdeps-4.2.x-1.$els.noarch.rpm
#echo Install the Zenoss dependencies - zenossdeps-4.2.x-1.$els.noarch.rpm
#try yum -y localinstall zenossdeps-4.2.x-1.$els.noarch.rpm
#echo "Installing EPEL Repo"
# JC - the regex epel* in the following wget also gets epel-rpm-macro which has new prereqs
# (as of October 2016) of 3 python-rpm-macros packages (see http://www.zenoss.org/forum/146626 )
# In fact, the epel-release package is in the 'extras' repo that comes with a minimal install of
# centos so you can just do `yum install epel-release` and avoid the wget too. (thanks baileytj)
#yum -y localinstall epel-release-6-8.noarch.rpm