Not sure about the metal roof?It does make sense if you have a wood stove and run the pipe outside.It's fireproof and acts as a brace for the pipe.I think it should run width ways to better channel water run off.
Caravan Gypsy Vardo Wagon: The interior of a #Gypsy wagon.
A Romany-Style Wagon, click to follow the link to the article. Isn't there one of these driving around JP? Or could we convert the Woodie?