The original design of the Adventure Trailer is South African based
http://www.bushmantrailers.com/
South African camper trailer manufacturer Conqueror produce 3 similar camper trailers in different sizes with the Desert Sky rooftop tent on top
http://www.conqueror.co.za/ one of which the Conquest is imported into Australia by Desert Sky Australia
http://www.desertsky.com.au/
As Bearfoot has said Backtrax Trailers have a top looking camper called the X-Terrain
http://www.campertrailers.org/backtrax.htm
I have seen where the guys in the USA get an ex-army 4x4ft amo trailer & put a rooftop tent on them.
Rob