The core of these were some basilisks and a rhino. Then everything was mixed up stuck them back together in unusual ways to make them all individual and looted. After the kitbashing of the main tank, lots of plasticard patches were stuck on to make it look a bit more orky. Attached with really big rivets, which are actually tacks... Then heavy battle-damage was added with an old engraving tool, modelling knives and pin vices.
Full post & pics: http://imperialgrots.blogspot.com/2010/06/basilisks.html