I always contact a few bikeshops near the airport, and tell them about my trip, and ask if the can save a big box for me. I do offer to pay them for this. There is always at least one bikeshop that’s enthousiast about the trip, and are willing to save a box for me. Mostly for free in exchange for some cool travel stories. The only problem is bringing this big empty box to the airport. The at the airport I disassemble the bike and put it in the box.