[Planecrazy]

Instead of attempting to "reinvent the wheel," you might want to consider looking at used Toyota Sunraders, or Winnebago Rialtas (based on VW vans). These are fully fleshed out motorhomes on a smaller scale, which results in better fuel economy without the hassle of trying to design and/or modify something to work in a way that's already been well thought out by people in the business.

I'm all about DIY, but it sounds as though you might better spend your money and time by grabbing one of these "classics" and then using your DIY skills by updating them to work better/more efficiently with modern materials and tech.

Just trying to help you think outside the box without reinventing the box! ;-)