I made a 1x4 holder for two 123 blocks. This has a flat bottom with holes, if you'd like this to work with Gridfinity, you can add footfinity pieces (see below).

NOTE: This has a modular “footfinity” base to save on plastic. Make sure to print some U shaped feet from this link. On a textured plate the 4.9 size worked great for me.

[https://makerworld.com/en/models/1183739-footfinity-gridfinity-with-smaller-feet#profileId-1194389](https://makerworld.com/en/models/1183739-footfinity-gridfinity-with-smaller-feet#profileId-1194389)