I've ridden to the airport with a rolled up bike box strapped to the rear rack.... Once you unroll them and tape the bottom they get 90% of their strength back. Helps if you can buy glass fibre reinforced tape, it's clear with linear (and possibly cross woven) glass fibres. It's strong enough that two strips adhesive to adhesive would be enough to suspend my 90+kg. Failing that, Gaffer tape is a good substitute. Takes me around 30 minutes to demolish each bike and get it in the box now I've had some practice.
Handy tips are:
Don't tape the top until you have checked in. Some airlines like to check you have deflated the tires, don't have a live tiger or a bomb in the box (you are suspicious...only a weirdo would travel with such a huge inconvenient box...)
Get some rubber chair tips to pad the fork ends, bottom bracket, axles.
Get some zip top sandwich bags to put small parts in, tape these to the bike, so if the baggage pixies hole the box, you don't loose them.
Generally it's easier to take the bars off the steerer and drop them along side the frame, install the cap on the forks so they don't fall out.
Taking the cranks off makes it easier to slide the wheels alongside the frame
I've installed self extracting crank bolts,makes getting the cranks of easy and saves trying to get pedals off.
Always get the biggest box you can, if you have to box, as it doesn't generally cost any more excess... 29er MTB boxes are great, my 26" Troll fits in one with the seat dropped and the rear rack and wheel installed!