How should I ask my boss for a promotion?

I’ve been at my job as a lab manager for over a year now. I was hired as a part-time employee while I finished my BA. Now that I’ve graduated from college, I’m ready for a full time position. More importantly, I really need health insurance. I’ve asked my boss twice before to be promoted to full time, and each time he’s let me down easy with a “hmm, we’ll see” type of answer.

I’m currently working around 35 hours/week at this job, and I feel that it’s only fair that I should be considered for a salary and benefits.

I have a meeting with my boss in about an hour, and I have no idea what to say to him. Any advice?