My daughter is right at the edge of our Keyfit 22's limit weight wise. I'm not sure if she'd be under 22 pounds on our return in a month. (That's why we are leaving our infant carrier at home).
I think I'd rather forward face, if necessary, on the plane, and have a better fitting car seat for all the driving we'll be doing on the other side of the world. Rear facing in the car won't be a problem.