I dreamt up some interesting fluff actually: the tank was a loyalist one that partook in an abortive invasion of a Daemon World within the Eye of Terror. This vehicle like many others was left planetside during the evacuation, and the same abandoned vehicles now fight for Chaos, in the legions of the Damned.
I should probably add that there is now a Flamer in the gun port in the front, and the rear has a door that looks like it maybe could work. I'll post pics when I've painted it!