The MX-5 trunk lid is bare metal, with a bunch of holes and exposed cables. I wanted to make it look nice, so I designed a panel without the use of sheet metal screws to attach it.
For my first prototype, I used a 3mm (1/8″) Hardboard. To make it bend in the middle, I made a 1.5mm deep V cut.
The panel was covered with speaker carpet, which I found on Amazon. For mounting, I designed a few 3D printed parts, including mounting clips. The lid has a few openings, which I used to hold the plastic clips (see picture below).
Amazon has lots of options for carpeting, but I think the best way to find it is at a local Car Stereo shop; this way you can check all the available options before buying it. I glued the carpet to the baseboard, using 3M adhesive spray, which I found is very good for this kind of work.
The attachment procedure is simple: First, the bottom clips go into the lid openings. Next, insert the two middle clips to the mounted 3D brackets, and slightly shift to the right, to align the top 2 holes. Finally, insert two plastic retainers into the top holes.
This looks good in my car, but extra weight is 2lbs (940g) and this is preventing my Trunk lid popper from functioning properly. To reduce the extra weight, I replaced carpet with felt and made the baseboard from a new material, which I found on Ponoko (laser cutting service company), 1.5mm (1/16″) Taskboard. This is a very light material, easy to trim and can be formed into 3D shapes.
Felt sheet – I used a felt sheet with adhesive on one side, which is easier to put on. The new assembly weight is only 11oz (300g) and it works with my lid popper. This looks great. The only concern is if it will be damaged somehow by big items in the trunk if it gets to poke.
Design files are available on the Thingiverse site.
Fully assembled version with mounting clips available from my store.