Many people are building their own bug out campers using a utility trailer as the base. Take a look at the various ideas people have come up with to build these. Some of them are very well thought out; with solar power, kitchens, bath etc.
If you already have a retreat location, one of these trailers would work well as a semi-permanent / portable base camp. You could live in it while you're building the main cabin and other retreat infrastructure. When you no longer need it you can use it for a guest cabin and still have a moveable bugout rig.
Even if you don't need or want a trailer; you can adapt some of this information and use it to build a small off grid cabin or 'tiny' house. This possibilities are endless.
6 x 10 cargo trailer to camper conversion
http://youtu.be/jpU450o6Zuo Cargo camper conversion: A 6'X 12' enclosed cargo trailer converted to self contained camper/boondocker/bugout vehicle.
http://youtu.be/LVTO2oIjq7s Cargo camper conversion build part 2
http://youtu.be/uPvB-971SqA CAMPER CONVERSION PT 1
http://youtu.be/TugbKpn1ohM CAMPER CONVERSION PT 2
http://youtu.be/TuYt39VGA1U 7 X 14 Trailer to Camper Conversion
Take a careful look at this one.
"I've seen a number of trailer conversions on YouTube, however this video goes into more detail about how this actually happens as well as using a number of atypical plans to keep costs down and design simple but just as effective."
http://youtu.be/CWjpFsjqSz0 7x14 V-nose cargo trailer
http://youtu.be/04wZvksZD6U Some things you need to consider before buying or building your trailer.
http://youtu.be/1IAZcvTd1SA