Every mount I have seen has a strength problem since the strength for the screws holes and strength for holding the projector are of different print orientation.
For holding the HY320 you want the strength in the rails which means printing vertically but for the screws holes to be strong you should print horizontally.  

That why I have decided to print it out of two pieces.
you can screw them together to the ceiling / wall or for even better strength you can glue them together.

Enjoy

I have printed in ABS without supports, 3 walls thickness and honeycomb infill in 20%