By papyrus do you mean DB 181?
This car was DB 181 originally, before becoming DB 350 blue, and now on it's way to DB 180 silver. Much of the undercarriage was DB 350, but there are nooks and crannies that were seemingly, to me, something like DB 181. But perhaps that was the primer.
What rust preventative treatment are people putting on the undercarriage of their cars post repaint? Preventative coating with Por15?