The XL size case from this set of 3x luggage would fit a disassembled 20" Dahon and wheels, according to my rough calculations. To be more safe, I would put the frame, fork, seatpost, handlepost in the L size case by themselves. And then put the wheels in the XL size case with your panniers. The B ware set goes for around $20. But supposedly 50% are broken because they're customer returns that they didn't bother checking before reselling. A new set costs around $70. The XL size is supposedly 1-2cm longer than the max 158cm linear dimension for standard baggage, but it might get past. You can take these and comfortably dump the cases on arrival, or else put it up on classifieds at the city you're flying into. I'm sure there are giveaway message boards. If it's a typical european airport that is close to the city center, people looking for free stuff can either drive there to take the cases from you or they'll take the train and meet you at the airport.
https://www.ebay.de/itm/RETOURE-3tlg...L/264355790323
I would wrap all the exposed corners in cheap pole protector foam that probably cost at most $10, and zip tie them together. You should probably ziptie the seatpost, handlepost, and fork to the frame so that they don't bang against each other. You can get a rear dropout spacer with a quick release for $10 meant for transportation, to hold the dropouts apart so the stays don't get bent. I haven't found a front one for 74mm, but you can simply use a M5x100mm (or M6, M8) bolt, 4x double sized washers and 4x nuts to hold the front fork apart.
I wouldn't check in a bike in a cardboard box. They will get smashed, dropped, etc. I had my bike fully assembled and folded in the original cardboard box once in an airplane, and it arrived with the lever bent inside out. Some airlines won't reimburse damaged bicycles if not packed and well protected inside a hard case.