I'm a woodwind guy and have the same questions. Unless your music just really calls for that "clarinet choir" moment (and if it does, you're probably amplifying it from the sideline) then I don't see a lot of reason to march bass clarinet. I also don't march bari saxes. Bringing the bari outside tears it up, holding it straight vertical to match the altos is difficult ergonomically, holding it at an angle so it can be played without causing tendonitis is impossible to clean, if you do actually hear it on the field it's probably not in a good way. Any kid who's typically a bass clarinet or bari sax player moves to soprano clarinet or alto/tenor sax for marching. I've also had a few pick up brass instruments instead - one of my best sax players was a sousaphone section leader by his senior year and made all-state on bari sax.