Should I tell my parents the truth?

I want to go on a one week trip with my boyfriend. We want to go camping & on hikes at the Grand Canyon. I'm 19 years old and have super strict parents. My parents don't know I have a boyfriend & don't know about this trip. I want to go even if they say no. I want to just talk to them about it but I don't think they will want to let me go since they don't even know my boyfriend. I'm scared to tell them about it because they might end up not letting me go but I will go even if it means "being rebellious" & just leaving. Or should I just lie & tell them it's a school trip? I don't know.