Question: Are you being paid for these gigs?
Im just wondering if maybe the band is not looking for a fulltime bassist, but rather just someone to play the shows with them as a hired gun.
Good question.
I think you need to talk to them and ask them what they are thinking. If you're willing, tell them you'll even hang around just as a hired gun for awhile, so long as you're getting your expenses covered in addition to a gig's fair share of pay.