I just installed a Kelderman
www.kelderman.com Air Suspension on the rear of our 2008 6331 Endura. Website has all the info.
Very well engineered, top quality fabrication & parts and straight forward installation instructions. The ride improvement is almost unbelievable! The install instructions & pictures were done on a Super Nova so that really helped. Here is a video showing the suspension at work that sold me.
Good company to work with and great price. Wish I had done this years ago! The hardest part was moving the wire and cables that would have rubbed on the new components. If anyone is interested in more info, please send a message.
Steve C. in Michigan