Never seen this before! Back in the day, was there a practice to fiberglass in a rubber tube on the inside of the early doors?

The doors are not rusted at all, so I assume it was done to strengthen the door panels. Anyone ever seen this before?

Also, quick question: Did the -6's come with the bottom of the engine lid painted black?

Thanks,
RLClick to view attachment

Body color under the engine lid.
PO's: who knows what they were thinking?