Hi there,
I am no expert but when i discussed a similar issue with my vet, she suggested that i avoid air travel when possible. She said that noise, plus unfamiliar surroundings, plus altitude, can be dangerous to boxers even when all precautions are taken. Of course there will be times when air travel is unavoidable but i still think that sea travel is less stressful to boxers and they can get to have a lot of fun with their owners on board. I have taken Martin on a boat trip that lasted for 16-18 hours and he was fine. We had lots of fun, he had lots of company, and he got to be with me. During the night they had an airconditioned crate compartment where you could lock your dog so that he would be safe and it was cool and comfy. The only problem i can see with that is potty breaks. I walked with Martin through the boat (heavily prepared to clean up the mess afterwards) but he refused to go potty for the entire journey duration. I noticed, though, that there where pet owners who had some special dipers that they placed on the floor and dogs did their business on them. As i said i am no expert but i think Martin liked the boat trip and wasn't stressed at all. I wish you best of luck with the move.
best
Irene and Martin