Hi Ken! I had an ancestor on site at that historic event, and collected a few docs several years ago.
This one doesn't seem to directly mention your ancestor, but might be interesting as it mentions the 12th:
transcription
Plan of Camp Defences Shewing the relative Commonwealth of Offices, Descriptions of Posts to be occupied, and the strength of each Post &c On the “General Assembly” being sounded, every Individual will immediately repair to his particular post, without any previous parade formation Extent of each command/Particular Post to be occupied/Strength of each post/Remarks applicable to Particular Posts/-General Remarks- Every party to be provided with an axe, and if possible same tools for making loop-holes. A member of Camp followers will be made available to act under the direction of the Commissariat Officer to supply the several Posts with Both Sacks, Tents & c. The Water Barrels are to remain full at Night and all spare Buckets should be placed All available Carpenters will have posts assigned to them, to be employed in making loop-holes, and strengthening the different positions. Responsible persons are to be appointed to take charge of, and arrange the issue of Ammunition. All Government Officers and Gentlemen not connected the Forces, who do not desire to remain in their own Residences, and having no appointed duty , will be good enough to repair to the Reserve The Women and Children will be sent to the Commissariat store Buildings The Utmost Silence is to be preserved by all persons, no talking above a whisper is to be permitted in the instance of necessary Commands in which case Officers and Non Commissioned Officers in charge of Parties, will speak in as low a tone of voice, as the nature of the service requires at the moment. Captain White and Ensign Moller / Rear Face of Camp: From Angle of fence adjacent to the Military Barracks, to the Police Stables Captain Holland Police / Right Flank, From Police Stables to Surgeons House Lieutenant Brodhurst / Right front of Camp From Surgeons House, to Officers Mess House Lieut Adams / Front face of Camp, From Resident Commissioners House, to Military Barracks Lieut Richards / Left Flank From Resident Commissioners House, to Military Barracks Military Barracks, Escorts Stables – Commissioners Stables, Blacksmiths forge, Police Stables Hospital Dead House Surgeons House, Mess House Line of Government Officers Tents Commissioners House, Court House JM Thomas Capt. 40th Reg. Commanding Garrison Cavalry Reserve The M.M Force and Mounted Police, not employed as above, will form in the Ravine between the standing camp, and that of the 12th Regt: The former facing towards, and protecting that part of the rear of Camp, The latter, a relative position to the Front of Camp. This Force connects the two camps. The Company. 12th Foot will Guard its own Camp detaching 1 Subaltern and 35 Men to join the Reserve at the Standing Camp M.M. Force – 26 Sabres Mounted Police 50 –do- Jm Thomas Capt. 4oth Regt. Commanding Garrisons Camp Ballarat 27th October 1854