When we bought our carseat we looked for safety, durability, and ability to do extended rear-facing (check out ERF here http://www.joelsjourney.org/). Little did we know we could be getting a monster carseat. We ended up going with the Britax Advocate CS. As it is a convertible that fits from 5lbs to 55lbs, we were covered and this is the only carseat we have ever used. Besides its size I really like it although Tim isn't a huge fan (simply because of the size)!!
Nolan and I are taking it with us on our first plane ride and checking it through. Since it isn't an inexpensive purchase and it is safety equipment, we wanted to be sure it would get there in one piece with no nasty stains or any structural defects. Of course NO carseat cover bags I could find in stores or even online would hold it. Eventually I contacted the manufacturer J.L Childress who makes a nice one that fits most every other carseat. They were familiar with my specific carseat and willing to make a custom bag to fit it. It is lined with padding even! Here are a few pics of the beast.
In the car we barely have room....
Now here is the carseat , the cover, and Nolan for perspective.
...and finally what I will be walking through the airport with tomorrow. It doesn't have wheels as the luggage tracks tend to rip those off and ruin the bag but it has a shoulder strap.