I guess I will ask are you just trying to travel with it or you need to carry it 4 miles in the woods, and if your are carring a 400mm that is not the Nikon VRII version my suggestion may not work?

If your heading into the woods this won't cut it but I use a pelican 1510 case. It was cheaper than many bags, I can use it as a carry on for most planes (except your smaller ones). Its water proof, says it will float but not about to test it. The case has a life time warranty, and I can put a pad lock on it. I would say the main problem is cutting the mold to hold the lens steady inside the case. It comes with foam that you can cut out for your application but I didn't use it. It comes with 4 parts of the foam, an egg crate part for the lid (2" thick roughly), two pick and pluck foam modules (2 1/2" thick each), and a thin part to cover the bottom (3/4" thick, which I did use)

I use this as my "long range" case. I have a D7000, 70-200VR II plus the removable foot, 17-35 2.8 (just in case something pops up close), 1.7 TC-E, charger for the D7000 battery, and the 400's massive lens hood. The mounting foot/bracket for the 400 stays on the lens. I have the lens coat and the travel lens coat cover on the lens/with hood and wrap this in a towel and strategically place everything else in the case. I will say it takes me about 5 minutes to load it each time but after tearing down a tripod/gimble head combo I just chalk this up as another step.

I use the tamrac belt at times so I have my each of my lenses in a "carry pouch" which gives them padding. If you use this option you need to add about 20-30 dollars for each lens pouch.

This is what I do but some may think of my as crazy to wrap my lens in a towel, but after I put everything else in the case its not going anywhere.

most of TT backpacks will hold the 400mm lens, glass taxi is nice, but IMHO streetwalker is better (bigger), especially when You need laptop

I have not used the Class Taxi but I have other Think Tank products and they are all very well designed and made

Does anyone recommend a case/bag to carry a 400mm lens? I did see the ThinkTank "Glass Taxi". Any others that work well? Thx.

OK,..I do realize I will get comments like,..."I'll hold it for you". haha. This is a serious question.