I have seen other stacking trays for the Raspberry Pi and liked the idea. I designed this tray differently so that I would have easy access to the micro SD card and better access to the GPIO pins. Also I made the base layer of the tray thicker so that it didn't feel as flimsy.
Minimal or no post-processing should be needed. However if you print in ABS the droop/sag of the first layers might require the holes to be opened up a bit.
I have included the SLDPRT if you want to modify this design or export the STL with lower resolution.