Any advice on convincing parents to get permission?

My boyfriend and I have been going out for three and a half years. We both live in Mexico City, he’s 23 and I’m 20. He’s leaving for Australia in three weeks, so we want to go to Cuernavaca ( a nearby city less than an hour away) for just one night.
Both my parents know him very well, and they like him. But when it comes to little trips like this, my dad kind of doesnt like it. Sometimes he lets me go and sometimes he says no. This getaway really means a lot to me and my boyfriend. Any ideas on how to convince him to let me go? Thank you!!!