Open car trailers are trailers made to carry cars, but have to walls or ceilings. These trailers keep the car open to the elements and have no security features. Millennium offers open car trailers made by Sloan. These roll back trailers allow the user to lock the wheel hubs, drive the tow vehicle backwards, and the trailer slants to allow the car to drive up on it. Open car trailers are the least expensive way to tow cars because they do not include walls and ceilings. Open trailers come in steel or aluminum frame with wood, steel or aluminum floors.