I made this with Openscad, so in theory it is parametric (haven't tested more than 1x1 as of now), just edit the grid_x and grid_y variables.

I recommend support for the upper overhang (also an issue I might look into).

Note: the gridfinity bin is required to be watertight, this is achievable by adjusting some settings (I recommend higher temperature, slower printing speed, higher extrusion rate, low layer height like .2 or .15).

Edit: I added a rim so that another bin can be put on top (useful for germination).