The original design worked okay, but I took a stab at making a few improvements:

1. Increased the diameter of the "nubs" at each end to 4.8mm, which fixed slop and tightened the tolerance of the overall height, for a slightly tighter fit.
2. Extruded the "latch" mechanism/curve by .5mm, which tightened the tolerance of the overall height, even further. It's a perfect fit now! By my math, that's .9mm tighter grip than the original model.
3. Curved the 2 long edges of the flat part, for a more ergonomic feel (this could easily be improved on, but this was my first time trying to curve edges).
4. Rotated the model so that it is ready for the print bed.

I printed it with support under the "nubs" ONLY.
You might get away with no supports at all, I haven't tried.
I printed with a brim for safe measure. If you trust your adhesion, you could print without.

I'm really happy with the results and hope you enjoy it as much as I do. It gives that relieving "pop" when it goes into place. I added these too, which all together make for a really solid seal
https://www.thingiverse.com/thing:2879391
I'm thinking of replacing my remaining 23 latches now, all in red...