Bag-it!

It's inevitable
Traveling abroad with your bikes can be a huge investment.
Either you go cheap by asking for a bicycle box from a shop, or get a luggage that is properly made for transporting your two wheels.
But before you commit, find out about the weight of your luggage including the bike to avoid excess baggage.
For economy-class travel, passengers are allowed to carry 20kgs of luggage. 
If you exceed the limit, you pay.
We've learned about this the hard way.

Choices
To be frank, there aren't many bags out there where you can pack a Dahon 20" folding bike.
I am very specific here. Just talking about Dahons.
So, for the frequent flier, Dahon came up with the Airporter and Airporter Mini..

Airporter-mini
This is a compact case to pack your 16" and 20" bikes folded.
But there is a catch. 
You must remove the wheels and handlebar for a snug fit.
If you have tonnes of junk on your bike like a set of racks, handlebar accessories, water bottle cages and other stuff, you would have to strip them for storage.
There are two versions of the bag. 
The older ones are not equipped with a TSA approved lock.
Newer Airporter-minis have packing instructions silk-screened onto its interior zippered compartment.
If you are a minimalist, the mini is suitable for the job.

The Airporter-mini

We found that the airporter-mini was not suitable to carry our 20" Dahon Speed P8 and TR, so, we returned it for an exchange with a bigger bag.

Dahon Airporter
These are the largest bags you can find in the market with a pricetag of RM990 a pop.
That's the price of a cheap folding bike.
I've decided that its best to invest on the luggage since we are doing some serious traveling with the bikes. 
We are thinking of cycling around the region, covering countries like Indonesia, Thailand, Philippines, Cambodia, Laos and Vietnam.
Ultimately, we will fly to outer Mongolia for an off-road ride in the Mongolian steppes.
The Airporter is by far, one of the most versatile folding bike luggage around.
You can pack a 16", 20", 24" and 26" bike in the bag. And all these are meant for folding bikes.
But before you do so, be prepared to purchase excess baggage - at least 10kgs of it.
Another way is to declare it as a sports equipment where airlines would charge a flat rate for it.
Also remember to deflate your bike tires prior to checking-in the bikes.
I am very happy with the Airporter because it performed flawlessly.

The full-sized Airporter with a Dahon Curve SL for size ratio

As for space, the Airporter is roomy, and you can pack your folded bike without removing its wheels. 
For bikes with the Andros handlebar, remove it from the stem so that you can pack it easily.
Bikes with telescopic stems and a clasp-locking handlebar had no issues fitting snugly into the bag.
We had a lot of junk on the handlebar and stuff like baggage racks. These could fit without the components jutting out.
And finally, as a word of caution: when you check it in at the airline counter, remember to lable it as fragile as most baggage handlers would toss the bikes.