For my Dahon MU D10 I had a bag made. I then cut up an old waffle style mattress topper and lined the bag. I took the rear derailleur off the bike and one of the pedals. Everything else stayed on. It is probably oversize but weighs under 30 pounds. I had thick web material sewn onto two sides from top to bottom for grab handles. Then I used just regular rope in an X type fashion to cinch everything up tight.

I have packed and flown it three times so far and no oversize charges yet. It is kinda clumsy to carry but worked great so far.