I used an Intermountain Husky Stack car for a 48' container. I cut off some of the bumps on the side and added some thin styrene strips on the ends, painted it black and added the hand rails. The LNG tank with the pipes on the one end and the other stuff fit into the 48' well. I think a 53' well, which is available, may be too long. I've seen where Walthers sells a 48' well modeling a Gunderson without the bumps on the sides.
http://www.modeltrainstuff.com/Intermountain-HO-47257-01-48-Husky-Stack-Car-CRLE-p/imr-47257-01.htm The sides need to be smooth.
I had to add filler to the well to get the tank to sit high enough. Link to
and you'll see, at the bottom of the page, a Chart Industries well car just like the ones that Chart is delivering to the FEC. I'm now trying to figure out how to cut the opening in the lower side of the well car.
I also have an N scale FEC LNG tender. I used an Athearn 48' well car for it.