I'd love to see what you have in the frame, any pictures? I'm trying to picture the first aid kit. I still have the steering tube free, but it's quite thin, so I'm not sure what I'd need in there yet.
I love touring on my brompton, in fact it's the only bike I've ever toured on! I'm too scared the airline staff will take my bike away at the gate, and it will be unprotected then. Not something I want to chance, I'll just keep watching the brompton mafia to see how they fare.
The box itself is 22" x 25" x 12" so a total of 59". The bag adds a little puffiness, but if they complain I'll help them measure and hold the bag tight to the box. I had one luggage strap around it, so that kept it more compact. There was no complaint this time though.