Expedition Motorhomes come in many different sizes and shapes.
The expedition vehicle Benzi in Lake Arthur, USA It is strange to think about that non are build in Iceland as it is very common if RV is build out for extreme situation that the first real test trip is taken to Iceland. That is thought to be the ultimatum of all test trips. I guess the variety of situations you can run into is to be found there. Icelanders travel more in 4 x 4 jeeps and are considered specialists in custom building them up to the point where we can drive them up on the glaciers in the middle of winter.
Benzi amongst friends of Benz and Unimog type in Panama
My ultimate expedition vehicle would be mixture of Icelandic, German and US knowledge mixed with some italian design. I would probably start with the guys at Arctic trucks for changes on what ever chassis I would choose, Unicat for the house and mixture of American things for the technology. Something in the direction of Earthroamer. I would probably look towards Italian interior design. If starting out again I would build it my self there are lot of sites to look to for informations regarding building your self. You can even by the house cut into the shape you want from foam board and then assemble them your self. These guys in Germany do that for you.
Unfortunately I have not found similar company in the US. One thing I would definitely not do is build out on a van type of chassis. It would have to be truck type preferably of the bigger kind. The only exception i might make from that is the sprinter from Mercedes Benz. Unfortunately Merchedes Benz do not have any big chassis at the moment, that i like, but that is not strange as they own the now Merchedes benz Unimog.
I recently heard about Fraightliner type that could be the one in USA and was told that the us company Eplorer was going to build theirs based on them. Up till now they have been using Ford 550 or 750. The Earthromer is based on Ford 550 to day. There is a lot to be liked about the Earthroamer, specially the interior and the technology. I still have to see about how they deal with the chassis, drive shafts, tires and stuff like that. For that I would probably trust the Icelanders best. Guys like Arctic Trucks or the Swiss company Achleitner that makes the Mantra.