The Rouillard Case is most compact of shipping cases

http://cellofun.yuku.com/topic/18525#.VKReLicqRzN

I travelled for many years buying seats until it was forced to be checked by overbooking. After that time, I used a number of shipping-type cases, and the best of the lot was the Rouillard. http://www.rouillardcases.com/#!our-products/c1w3p I see that one of the links you saw doesn't like, and I will explain why that person doesn't know what they are talking about.

No insulation will keep the cello warm, the cello does not generate heat, unlike your body, and insulation will not generate or preserve room temperature. Foam padding is not an insulator, regardless, so that alone is totally BS. When I first saw the maker demonstrate the aluminum case, he put a guarnieri cello into it, closed it, and then jumped up and down on it (it was lying on its back). No problem. The problem that any case will have is if the neck or pegbox is restrained in any way. If the case bounces or is significantly dropped, the body of the instrument can move around a bit, but the neck will not, therefore, it can break off. You can imagine how I know this. This did not happen in the Rouillard case, BTW. The Rouillard is the most compact of any of the shipping cases, which makes it easier to handle, and it is made of exactly the same materials and density as the airplane itself. It has wheels which can be removed and stored inside the case, making it less likely to get caught in any automated systems. As to the case scratching the inside of a vehicle, I have experienced this in regular hard cases, too. The cello was not designed to fit cars, it was designed to be an instrument. Any sharp metallic pieces (or fiberglass, etc.) can be smoothed with super-fine polishing grade sandpaper. Yes, they use this stuff to polish automobile paint, so relax.

Airline policies and the regulations that govern them are changing slowly, and almost any airline will have their own rules posted on the luggage section of their website. here is a link that addresses some of this

http://www.tsa.gov/traveler-information/musical-instruments

https://www.futureofmusic.org/article/fact-sheet/traveling-instruments

http://internationalmusician.org/instrument-carry-on/