I converted a Ford E350 15 passenger van for a school once. It was fairly easy to do - the adapters, fenders, etc, are all readily available. Total cost about 5 or 6 years ago with all new wheels, tires, etc, was right at $2800. It definitely handled safer, especially loaded with 15 people and inexperienced teachers driving it. It did loose about 1 mile to the gallon though. Which in those rigs is about 8%.