While printing the left and right assemblies make sure the cross bar connector is facing up. While placing the crossbar make sure that the extrusions on either side are flush against the print bed. When properly placed no supports should be needed.
In order to fit the left and right assemblies on the Prusa i3 Mk3s print bed I had to disable the skirt. Other than that every thing works as expected.
I printed this in PETG at 0.2mm layer height. Other plastics may work as well.
I printed using 6 shells and 6 top and bottom layers.
I used some super glue to attach the middle bar to the right and left assemblies. The extrusions will make for a snug fit but I would rather air on the side of safety.