Yahoo Message Number: 106616 (http://groups.yahoo.com/neo/groups/Country-Coach-Owners/conversations/messages/106616)
I had a similar issue with a black line appearing on the floor and on the back wall of the closet. I found pin hole leaks on the muffler which let exhaust escape into the engine compartment. I replaced the muffler and that solved the issue, with no more soot caused black lines in the past 15,000 miles.
Dennis 2003 36' Allure #30884