@HayiWena Yeah, we (over)thought about this, that most trombonists really need to be in a box, because the back bench of a GSD/longtail perches them up there without the ability to hold anything for balance.
That said, we had one awesome trombonist who declared up front that it was his "dream" to play facing backward on a longtail, and we made that dream come true. We also stuck a claronet player who didn't RSVP on a GSD, as well as a trumpeteer on an extracycle