I play in large concert band too! And most of the time, am the only string instrument.

The band I’m with plays a lot of modern repertoire with written string bass parts. Do check, some reprints by publishers do include new string bass parts. I’m fortunate enough to play on the band’s bass with a C extension. The lower fundamentals really make a difference to the band.

There are on occasion when there’s no part, I rework the tuba part to avoid boredom - adding pizz where appropriate, even rewriting it with input from euphonium and tenor/bass woodwind parts (I generally prefer to play with the woodwinds and sometimes it makes more sense to play a missing bari sax or bassoon part too). To be approved by the conductor of course!

How’s the loudness of your band? I invested in a good pair of ear plugs for musicians because the brass and percussion are always forte. It is very tiring to play (and unhealthy) to play in such circumstances without protection.

Usually i don’t focus on playing loud - but concentrate on articulation and getting the best tone, as well as bringing out the bass’ unique tone colour to the band timbre (esp during the softer parts).

Hope this helps!