finally made it to the flaps and saw this at Advance Auto:
http://www.designengineering.com/category/catalog/design-engineering-inc/component-specific-products/versa-shield

That looks like what I will try for insulating the hot exhaust pipe
where it comes up out of the fiberglass-inside-sheet-metal-column all
the way to the end at the van's sidewall. Unless someone shouts out
"No don't do that!"

Edward