Trip with Boyfriend?

So my boyfriend, his cousin, sister, and brother in law planned a trip to Disneyland and invited me to go along. I really want to go, but I don't know if my parents would allow it. I'm 18, but I still live with my parents and they are kind of strict when it comes to stuff like this and on top of that we've only been dating for 3 months. The trip is in a couple of weeks so I have enough time to save up so they can't say they won't give me money for it, but I don't know how to approach my parents about it. How can I convince my parents to let me go or is it not a good idea to go on the trip?

UPDATE: my parents said yes!!