Thanks for the interesting photos. Always the skeptic, I have to take issue with the authenticity of the carriage in the second photo. It looks like one of the bosses told the workers "Ok you blokes, get cracking and make up a fitting carriage for this little tube so we can fill that vacant spot on the display floor."
The axle looks like about a 3/4 in. dia. shaft, and it looks like they used sheet metal for the sides of the part connecting the gun to the front of the trail. Pretty amateurish. I'm not saying that carronade was never mounted on a field carriage, but I hope if it was, the carriage was constructed more substantially than the one shown.