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Haven't tried one yet but...
Many bass trombone players I know (including myself) have switched to Griego mouthpieces with excellent results. The Griego Deco .5 or .75 may be just the ticket if you don't have to have stainless steel.
A tenor playing friend of mine just got a G&W and he loves it, but prefers it more for bigband and commercial playing, I am not sure what model he has.

Marty "Who wouldn't mind trying a G&W bass bone mouthpiece, if someone around him had one." Neilan

I am using the G&W Churada on my Doug Yeo bass trombone. It is their smallest tuba mouthpiece but my bass bone has never felt or sounded better. I got the idea from Tommy Johnson, who also uses a tuba mouthpiece when he plays bass and contrabass trombone. The low notes pop out like I'm playing my Yamaha 621 F tuba and I can still sore in the upper register, having no problem playing up to the Bb above middle C.

The Yamaha Bass bone has a receiver that fits the Churada perfectly.