I have never seen a bass clarinet in a marching band. Tenor sax, yes. Bass clarinet, no. I can't imagine why anyone would march a bass clarinet. They're heavy and seriously impractical. Might as well ask a student to march with a contrabass clarinet! It's about as practical as marching a bass. Sousaphones are large and unweildy, but at least they're made for marching.
A bass clarinet does provide much needed "bottom" for a concert or stage band, however. In that environment, they are wonderful and they shine. There are some concert pieces written for bass clarinet and in a concert band setting, they make for entertaining listening. But marching one? I don't think so.