Not sure what the temp range is and I only mention Rustoleum because I read it here someplace. I had considered using liquid tar but again am not sure about the temp but it would probably smoke some at first and then lay down a gooey coating that would keep the moisture off. I read that Honda coated the inside of some of their exhausts with some sort of asphalt and it got me thinking. I was hoping I would trigger a discussion and someone would know more about it or had done it successfully.
"66CL160, 68CL125A, 68CL450, 69CL125A, 69CB750, 71CB450, 71CB500, 71CB750, 72CB350F, 72CB750, 74CB750, 75CL360, 75CB550, 75CB750, 76CB750, 79CB750, 79CBX, 79CBX, 80CBX, 82CB750, 84VF700S 05HDSPORTSTER1200ROADSTER"