This is an egg tray I designed for my sister's fridge. It was 5x2 originally, but I decided to parametrise it in OnShape. You can find it here: https://cad.onshape.com/documents/7ac371b5806469f08126c29a/w/2156570f9897e4d594a6cff8/e/e5977b458e3c852f402b43bf

Here you can find STL for all sizes between 2x2 to 8x3. If you need a different size just leave a comment and I'll add it.

Walls are 2mm thick, and the base is also 2mm thick. It's solid enough with that thickness.

I printed this with a 0.8mm nozzle with 1mm line width and 0.5mm layer height, so the base is only 4 layers and the “support” is only 2 walls. I printed it at 40mm/s because I didn't push it too hard, but it's an easy print and can print faster if your heater block can sustain the temperature.