
Looking at the sprue shots and the instruction sheets for this new Hobby Boss offering it would appear that they have created some sort of domed metal "weather cover" to go over the gun ring opening in the roof of the cab.
Correct me if I am wrong but I do not believe such a device ever existed. Every enclosed cab vehicle outfitted with the opening for the gun ring that I know of has had a canvas cover that tightly tied with a draw string around the outer lip of the circular cab roof gun opening.
I have seen some canvas covers that also have a single bow (wooden I assume) that is snapped into the inside rim of the cab roof opening that then arches upwards to give the canvas a bit of an arch to better assist in water run off.
I do not know where HB got their reference for including a domed metal lid to cover this opening. Perhaps I missed this detail during my research.