Custom & "Spec" Trailer Builds Can't find exactly what you want? Let us bring your vision to life. We design and build fully custom Diamond C trailers (also known as "spec" builds), managing the process from concept to completion so you get the trailer you've always wanted. Central Trailer Sales, in business since 1995, is a locally owned family business. We have been in the auto and trailer business for over 25 years and have built a reputation for providing the best value for our customers.