When Markos and I looking to making these, we learned that the original part was round, and was designed to be stretched into an oval shape. It appears they were injection molded parts. As the original parts aged, they lost their elasticity, returned to their original round shape, and no longer stretch sufficiently. We were looking to make a computer printed substitute with a more oval shape.
These not only need to stretch into an oval shape to mold over the mounting plate, they then need to bend to the contour of the trunk and retain a consistent lip around the outside of the plate. (And whatever material is employed needs to remain color fast and not deteriorate when subjected to UV). Finding an appropriate material for the part was the reason Markos and I never finished this. And to make matters even more complicated, I believe there was some sort of environmental concern either with the original material or the manufacturing process, so this new part probably will differ from the original.
In any event, I ordered three of these as a test to see if they are correct. I'd be willing to order another 20 if these are good.