Possum:
I have never heard of the north or the south using a unpainted gun carriage. Using paint on the wood or metal was a preventive measure to protect them. All references I have seen mentioned carriages as painted. If any were used unpainted, it could only have been in an emergency situation and not common practice. My best advise is to say that it would be more historically correct to paint them as outlined in my previous post.
All reproduction gun carriages I have seen, wood or metal, are painted as described
Ron