Remember the box you got the AT Pro in? There was alot of empty space in that box. Remove the coil, and remove the shaft. The shaft will collapse down to about 2 feet or so, all will fit into your carry on luggage. Still room for your pinpointer too... just put the diggy tool in checked luggage.
Garrett makes a soft case for the AT Pro which is actually quite nice. It has shoulder straps so you can hike with the detector like a back pack, or you can carry it like a rifle bag. It's well padded. I expected it to be junk but it is not at all.
I have one and although I haven't found a need for it yet, I do like it.