Based on the measurements, Jason Carson created this simple trapezoidal shape out of 1/4-inch MDF. He then attached 3M double-sided body tape to the pattern. Then, the pattern was stuck to the other roughed-out pieces of 1/4-inch MDF. The entire assembly was then trimmed out on the router with a flush-trim bit. This ensures a perfect copy. If you don't have a router, this can be done with a Roto-zip or Dremel with a flush-trim bit (always with a bearing!). Or, you can use a jigsaw and some sanding, but they won't be perfect.
Another piece of 1/2-inch MDF was cut and laid out on the base. The pieces that were just made were measured and placed in the correct position on the second base. Then, the trapezoids were traced onto the base. The interior of the trapezoids were marked 1/2-inch inside the outer line. The base was placed back onto the trunk lid and additional MDF was used to create the cover for the latch. No brad nails were used in the build of this piece; everything was glued together with superglue.
This shows the trim for the trunk latch. The goal here is to minimize the gaps, which will swallow up large amounts of fiberglass-reinforced body filler. The interior was trimmed out from both the second base and the main base. This was done to make mounting the panel easier and to save some weight.