Here is the patent information on the rollback trailer. http://www.freepatentsonline.com/5092623.pdf
Maybe you can get some information that'll help you by downloading the sketches and description of how it works.
The patent was filed in August of 1990, which means it would have expired in August of 2010 under the standard 20 years from date of filing rules of the USPTO.
FWIW, it is a violation of Federal law to make a public claim that an item you are selling is patented unless that item is indeed covered by an active patent. Perhaps A Bar D would like to come back and show a reference to some other patent he holds exclusive rights to since it appears this patent by Melvin Swanner, which he refers to on another forum, would seem to be in the public domain.