Haven't had time to get any progress pictures yet, but I have developed my own better means of making a similar one. So far that is done is a custom made tank with trigger system and barrel mounted to that. All that is left is to make the trailer and get the axle in(still waiting for it after ordering). The overall length of the actual cannon from (a very unnecessary) flash hider to the breech load cover at the back is a good 7 feet.
On the tank is a safety release valve, main airflow(into trigger system) and nipple to fill.
The trigger system to barrel connection was one of the hardest to overcome since smoke stacks aren't found everywhere and are not cheap.