Haulmark, Interstate Cargo and the Carry-On Trailer Corporation are three manufacturers of 6-foot by 12-foot enclosed cargo trailers. Each manufacturer offers different options and specifications for custom-built trailers.
Haulmark offers five models that come in 6-foot by 12-foot dimensions: the Passport, Transport, Transport V-Nose, Cub and Grizzly Cub.
Interstate Cargo makes the Victory, Loadrunner and Pro series. These trailers cover a range of uses from light-duty and recreational to heavy commercial use.
Carry-On is the largest trailer manufacturer in the United States as of August 2015. It sells the widest range of sizes and specifications of enclosed trailers as well as parts and accessories.