This relates to our Kickstarter, and covers both PrusaSlicer and Cura approaches to printing the objects without supports.
I’d strongly suggest using PrusaSlicer (which works with machines other than Prusas, including Enders) given the added convenience of the ability to choose the bridging angle as you’ll see below.
By default, most slicers seem to use 45 degree bridging angles, which produces bridges like this (light blue):
This will produce a droopy print in the rectangular cutouts. By changing the Bridging Angle under Infill in PrusSlicer to 0 degrees:
That gives us overhangs like this:
The overhang is quite short and has been managed without supports on all the printers we have tested.
Cura lacks any ability to manually alter the bridging angle as far as I can tell, but you can get around that by rotating the object itself 45 degrees. By default the overhangs look like this:
Rotated 45 degrees gives this:
This will cover both the recesses for the floor tabs and things like the window base in the building.