I had an upholstery shop build a cordura bag for my Dahon. I lined the bag with a cut up mattress topper (looks like an egg carton). I remove the derailleur and pedals---I hate folding pedals---and put the bike in the bag. I have taken it on 4 airline trips so far with no issue. It is oversize (no one has ever measured it) but under 30 pounds and I have never been charged oversize.---Someone on this forum suggested that.

I had straps added to two sides of the bag that are sewn in every 8 inches or so. I use regular cord and double X the bag to tighten it up and give the handlers even more to grab. I put cardboard in the middle of the fold to keep the bike from chewing on itself.

I have walked about a mile with it once balancing it on my suitcase. Yes it was work, I am going to have a handle put on it right next to the closure to make holding it on my roller bag easier---. I might add a way to bungi it to my regular bag.

I have the Mu D10 (among other bikes) that I travel with. I would not buy a Dahon below the 8 speed Speed frame. (no Boardwalks for me---grin) I have stated this many times but with small wheels I want to use a standard 8, or 9, or 10 speed
cassette with an 11 tooth sprocket and I prefer a 52-56 front sprocket. The main thing I have against freewheels is the smallest cog generally is a 13 which gives you too low of gearing in my opinion. If you like to getiton at all you will not be happy with a 13-42 or 13-46 which are common on the 7 speed bikes.