The topic that got me started down the path of "another vehicle" was the question of maintenance and repairs. Our Tiger-Chevy Duramax was incredibly reliable in South America, BUT it was clear from conversations with Chevy dealers in various countries that repairs on the engine/transmission would have been very difficult. Those vehicles, the Duramax engine and Allison transmission are not used in any commonly available vehicles in those parts of the world.
The situation seemed no better with the Earthroamer's Ford chassis. Dick Smith's experience with his 6.0 PSD Earthroamer in Mongolia see this link may be an extreme; but unlike Dick we don't have the money to fly Ford mechanics from the US to fix mechanical problems.
It is worth noting that the Smiths and their Earthroamer did complete their trip around-the-world and at least one other Earthroamer see globalroadtrekker.com is currently undertaking such an adventure. So my concerns may well be "obsession" rather than realistic.
Vehicle GVW, tire load rating and suspension modification was the second topic that got me thinking of "another vehicle".
Our Tiger was pretty much at maximum GVW all the time. That was not a result of us carrying a lot of stuff simply the result of the camper body on a 1-ton pickup. The consequence of that loading was that at the rear the tires were running at their load limit and wore relatively quickly. Had I stayed with the Tiger I would have considered an upgrade to 19.5" wheels like the travelin-tortuga.com , but that may have involved some suspension mods and maybe re-gearing.
Our Earthroamer was also running close to GVW but at least with those 22.5 wheels and Michelin tires there was plenty of excess tire load rating.
I concluded that I should look for a camper built on a Mercedes truck with a GVW of over 20,000 lbs, tires that could handle our traveling weight and the vehicle GVW and no suspensions modifications.
The most colorful explanation of this I have ever read is from Jim Rogers. He and his wife drove a yellow Mercedes sports car around the world in 1999, 2000, 2001. He argued (something like) "when dictators take over a country the first thing they do is buy (stolen) Mercedes cars". Hence even poor countries have Mercedes dealers.
It is (probably?) not true that there are Mercedes truck repair facilities everywhere, and a Unimog is only a "sort-of" Mercedes. But I still bought the argument, that a Mercedes truck will be easier to get parts for than a US Ford or Chevy.
In August of 2011 we visited the GXV factory in Missouri primarily to look at their Global Traveler vehicle.
This is a "typical" European style expedition camper; a forward control truck with a camper box on the back. The truck itself was a Mercedes 1017 with factory 4x4 and factory rear locker. The only modification to the truck was a conversion to 20" wheels all round and singles (rather than duallies) at the rear. This truck is commonly used by Europeans for expedition campers so I felt confident that it was a good candidate.
In the flesh the truck was less than I had hoped for. No creature comforts (the F550 Lariat package on our ER had somewhat spoiled us) including no A/C and no cruise control. A bit low on power and gearing for extended highway travel.
If we chose this option GXV would have to source a truck for us in Europe and import it under the 25 year rule. The all up cost to get a 25 year old truck was approaching that of a new F550.
All in all the truck was not as strong a candidate as I had expected. But the camper box itself was great, well made with plenty of storage and top line equipment.
The only other realistic option for a "Mercedes" here in the US was a Unimog U500. We knew from previous conversations that Mike was very familiar with the U500 and thought very highly of them. Nina and I on the other hand had viewed them as a bit O-T-T (over-the-top).
While discussing all of this with Mike and Rene Van Pelt they mentioned the vario-pilot feature available on some Unimog U500 trucks.
For those that don't know about this (as we did not at the time) it is a little un-believable. It is a feature that allows the driving controls (steering wheel and pedals) to be moved from one side of the vehicle to the other. Moreover this transformation takes only a few minutes.
This gave us the option to take the truck and camper back to Australia with us as the vario-pilot qualifies as right-hand drive. Other vehicles like the Chevy or Ford would probably require a steering conversion to be eligible for Australian registration.
The vario-pilot was a significant factor in our final decision. Whether we will eventually take our U500-GXV back to Australia or not only time will tell. But the option to do so seemed valuable.
Just to complete the picture. The U500 has a 33,000lb GVW, is factory 4x4, and comes with 395/85R20 tires which will carry the 33,000 GVW easily.
So in late August 2011 Mike with the help of Rob Pickering found us a U500 with the coveted vario-pilot and we were on our way to yet-another-expedition-vehicle (YAEV in the language of linux nerds).