Seasonal hiring: what is paying well this year? (update)

A staffing agency says some roles convert to permanent after 18 weeks. There are 18 people counting on me, so I am trying to be careful. I would like to avoid a gap in my résumé. Has anyone been converted to permanent?

Thanks for writing this out. I went through something close to it 10 months ago, and it got easier once I kept a simple log of every call and form.