On unfamiliar gigs such as this,
I've told band leaders upfront that I see bass solos much the same as I do drum solos:
One a night is enough.
Then pick a tune you are comfortable with to take it.
Watermelon Man is an easy one as far as changes go
and Summertime is another one of my choices.
Of course there is the old line,
"Bass players. We never solo, yet we always solo".
Following this approach,
when they turn and ask if you want one,
simply yell,
"I AM soloing!"