I have not yet had an occasion to travel with my Dahon, but here are some packing schemes & tips proposed by one of the online Dahon dealers:

softside case with DIY protective shield:
http://www.gaerlan.com/bikes/case/case.html

packing in a hardsided suitcase, such as a Samsonite Oyster:
http://www.gaerlan.com/dahon/pack.htm

If I ever travel with my Dahon, I'll probably be referring to one of these.