Taking Photographs at Hampton-in-Arden in 1875

This extraordinary contraption appears to be a portable photographic darkroom belonging to James Green (on the left). At the time he lived at Goodrick Street in Birmingham and later moved to 132 Great Lister Street. He and Henry Coley (on the right) took it in turns to pull this cart from Birmingham to Warwickshire villages and back home again each day to ply their trade. They must have been extremely fit! This photograph was taken at Hampton-in-Arden in the summer of 1875.

Please can someone suggest how this worked? It looks as though the cart provided a dark room for one man to stand in and develop photographs on the spot. Would this have been feasible? (And if so could it be counted as the precursor of Polaroid photography?!)