I designed this cart storage module for my limited cart collection, it’s handy for sitting next to my computer when playing. I sized the holes just big enough to fit the AVGCART so it will hopefully also fit SIDE 2&3. Normal carts obviously fit fine as well.
The back has a matching angle to the front so it should be modular although I didn’t take any particular steps to be interlocking.
You can order this file, printed by me from my Tindie store.
If you have a 3D printer and want to print this for yourself, you can download the STL file here