Over the course of about a year I took a brand new cargo trailer and did a conversion on it. Complete electrical, heating, air, and plumbing system including waster water storage, bathroom, and also an integrated Onan generator. While a bunch of fun it didn't come cheap.
Here's a link to some of my projects during conversion.
Window Installation http://toponautic.blogspot.com/2014/01/diy-cornernew-install-of-rv-type-window.html
Roof Vent installation http://toponautic.blogspot.com/2014/01/diy-cornernew-install-of-rv-type-window.html
LED Indicator Light http://toponautic.blogspot.com/2013/09/the-diy-corner-led-indicator-light-for.html