I received the Metra dash kit with my Kenwood double DIN head unit and found it quite frankly to be a flimsy piece of junk. After searching around on the internets it seems there are no better options for the Mazda NB MX-5 Miata.
So I decided to make my own.

This design borrows heavily from the Metra kit, but has a few upgrades:
First, I hated how the sides, which are screwed to the radio, didn't rigidly attach to the faceplate. Not even a snap fit. They're somewhat constrained when the radio was inserted, but they were still loose. And it didn't feel secure for a car that's capable of >1.4g.
Second, I disliked not having any real fastening to the dash. The Metra kit only had the 4 locking tabs. And the entire radio bezel sits inside the dash trim ring, so there is nothing keeping the radio from falling out or being stolen in 5 seconds other than the locking tabs. I wanted to retain the screws for the stock mounting holes. I've also retained the locking tabs, but found they're redundant and the screws are much more rigid.

This will fit the NB1/NB2 (NBFL) Miata.