I've had to miss class for random reasons every now and then, but never a whole week all at once. My classes move so fast I would get lost!
Most professors won't give you a hard time, but there are those select few that think their class is the only thing in the world that matters!
I would just make sure you're not missing any tests, and that any in-class assignments can be turned in before/after the trip. Also, tell your professors ASAP, they'll appreciate that you're planning ahead.