Not much really. I only saw it once.
He used a old trailer dual axle that he got for cheap. Placed a few cabinets in the front to cook on and use for storage. Did some insulation on the walls and ceiling.
Added a plywood bed over the wheel walls that he takes up to put the harley in. That's about it.
You could get a smaller trailer with single axle and side door and a really neat job with it. Open the back and still have the kitchen there and do what ever you wanted to the inside.
Would all be up to you as there aren't many pic's of something like this.
Would make a great addition to this site to see someone do it.
Bufordt

"RUSH" The Man, The Legend, The Way Of Life.