I designed many mouthpieces for my tenor trombone until now. This one is the best one for me - maybe you just try it and leave a comment!
I wanted to rebuild the 6BL mouthpiece of one of the best mouthpiece manufacturers, but as you know this 3D printed mouthpiece is nothing to compare with the "real" one. But obviously it is not bad if you play outside in the winter ;-)
Place it with the "lip side" on bottom for printing!
Produce a smooth surface for your lips
Don't forget to sand the parts of the mouthpiece which get in touch with your lips and also the shaft!
After sanding you should use a plastic polish to get the surface as smooth as possible!
(I always sand with different roughnesses: 320 / 600 / 800-1000)