How do I ask?

So I have spring break in March and my boyfriend wants to take me to Destin,Florida. We would be going with another couple and I'm super excited. But my dilemma is asking my parents if I can go. I'm 20 years old and I live with my parents. I'm a junior in college and this would be my second trip with him. In September they let me go to Texas for 3 days with him. This would be an almost week long trip. How would I ask my parents? They're not super strict or anything.. I'm just scared they wouldn't let me go and I want to go so bad.