I am looking into this style of pin box Demco "Glide-Ride" king pin. Less items to fail and no maintenance required on the unit such as maintaining air pressure. This was recommend by two members from Turbo Diesel Register forum, that I am a member of too. I have attached the web site for your review.
http://www.towdemco.com/glideride/glideride.html
They both pull heavy 5ers and have this style of pin box on their units. In fact one of them replaced his "TrailAir" 5er pin box with the Demco "Glide-Ride" king pin box.
Jim