Do it yourself!
My own introduction to camperizing came when I decided a campervan would be the ideal vehicle for my young family. I'd hit upon Sportsmobile, and their amazing vehicles, but couldn't afford one for myself.
After looking at many pictures, and reading about their strengths and their shortcomings, I decided I could convert a Ford E-350 for a fraction of the price, and using my preferred materials.
I had no carpentry experience, no electrical experience, and I'd never upholstered a thing. A few months later, I had built cabinets, drawers, beds and couches, and wired in an electrical system that included a large solar panel, shore power, refrigerator, and a house battery.
The main factor in my build's success was extensive research. I spent many weeks reading every book and website I could find on the subject, and in doing so avoided many of the pitfalls that are out there. Pre-planning your build is crucial. Instead of keeping this information in my head (and therefore likely forgetting it!) I've started putting it down on this site.
This is just a beginning - I'll add many more pages as I have time.
Good luck! Building your own van is a great experience, and you'll end up with something undeniably your own. Whether it's the most basic of setups, or something fancy and incredible, enjoy the process and enjoy the end result.
Cheers!
Mike.