I want to create a mobile art therapy studio in the back of a box van to make it easier to get to my clients with all my equipment and have an uninterrupted space to work. My criteria are: 1. maximum space in the back to create an office type room including insulation, a window, and a sink. 2. best fuel economy (I will travel to 2-3 locations daily within a 5 - 25 mile radius). Reliable for many years.