I think Mac will truly custom-build anything you can think of. A coal hauler just north of here got them to build him a couple 48'x102" dump trailers with 100" sides with four full-time axles on Canadian Reyco suspension, and they warrantied like it was a regular old 80k gross dump trailer, no big deal. They won't even think hard about wood floor and container locks.
I had a Wilson combo 48x102 step and really liked it. The trailer was 10,100lbs with 2 boxes and all alum wheels also came with the rear axle dump, load gauge and has a deck height of 39.5" on 255/70-22.5's. Also the shop in Sioux City is really good and the people are good to work with.
I had the trailer from 05-10 and never had 1 problem with it and after running all over there 48 the powdercoating still shined like new on the main beams and the trailer had no rust.