the variety of points of views of those of you who have travelled a lot
IMO, you are on a good path. You'll learn more--quicker--that is directly relevant to your challenges from people who have been there.
You will probably not achieve the unanimity of opinion and definite, clear-cut answers that you are hoping for. Overlanders are a bit like economists: "Ask two economists for an opinion and you'll get six." That trait is consistent whether it's on an overlanding forum or around a campfire in Peru.
We built a truck to explore South America and spent a lot of time in the areas you are headed. I also interviewed most overlanders we met along the way, many of whom had also spent extended time in the areas you plan for your expedition.
Full disclosure:
- We used a 2007 Fuso FG (4x4) chassis, so I have more direct, personal experience with that chassis than any other in the region.
- We spent a lot of our time in South America in the Andes highlands, so my experiences are skewed to the altitudes, environments, climates and peoples you will encounter.
- I wrote a book about the last day of the Atacameños civilization while we were there, so my enthusiasm for your mission may show through in my recommendations.
Following are my observations related to your challenge:
Engine -
Diesel is your only practical choice.
You must have a turbocharged (or supercharged, although I am not aware of any modern examples relevant to you) engine due to the elevations you will be traveling in.
Chassis -
- The most important day-to-day dimension is turning radius.
- The second most important dimension where you are going is track width.
- 4x4 is not nearly as important as you think it is for most of your utilization.
- Manual transmissions are serviceable, automatics are very rare.
Payload size -
- Height is not as much of a limiting factor as you would think. There is a definite practical limit on length. Width and height will be an issue in small villages and some market towns.
Capacities / Duration -
- We found the ability to camp for a month at a time to be well suited to the region.
Parts / Service -
I did not observe one, dominant brand in the areas you are headed beyond the typically ubiquitous Toyota HiLux. Among medium and large diesel trucks, several popular European brands, e.g. MAN, Mercedes, etc. are not well represented, especially in rural areas. As is true in the rest of the world, any vehicle has region/market/country specific parts, so you will probably need to ship in parts no matter what vehicle you utilize, even a classic round-nose Mercedes. The most popular mid-size chassis are used for the village-to-village route chicken buses. When we were there, these were overwhelmingly based on the Mitsubishi Fuso chassis.
Energy -
It is always a good idea to have multiple ways to accomplish anything: heating, cooking, etc. This implies that relying exclusively for any one energy source for any key aspect of life is not a good idea in full time overlanding. Redundancy is a very, very good thing. Availability of energy types in your target countries varies. For instance, in Peru, you can refill LP/LPG/Propane at a gasoline service station directly from the pump. In Ecuador, this is not possible.
Full time living and working -
People can put up with just about anything if they know it is for a specific, limited duration. Even so, putting up with uncomfortable living and working conditions has a negative effect on productivity and can also have negative effects on morale, teamwork, etc. You can definitely create opportunities for team bonding by extreme conditions, but your overall scientific / information throughput and output will suffer.
Mobility -
For a team of four to five, having two vehicles, one of which is a 4x4 HiLux, could be an ideal scenario. Anything bigger than a HiLux simply can't get back into or even close to some of the sites you will want to document. Trying to live, work and be productive out of a HiLux sized vehicle for months to years at a time is challenging when you focus on the "sustainably productive" aspect. I suggest a medium or large truck as a basecamp vehicle and a 4x4 four-door HiLux as your scout, run to the village for pan, commute to the work site, etc. vehicle.
What all this means to you:
1. You can find diesel anywhere you want or need to go.
2. Due to current ultra low sulfur diesel fuel requirements in North America, you must utilize a 2007 or earlier North American market chassis. An alternative is to ship in your payload and use a local chassis.
3. Large trucks do not work well where you will be living and working. Large trucks have a wider track width. The bridges where you are heading are all built to support the chicken buses. Consequently, a medium duty truck chassis, which is what the buses are built on, is your best choice. We know of multiple large trucks that broke through narrow tracks in the areas you are headed. For roads/tracks off of the chicken bus routes, every dimension and capacity is optimized for the HiLux chassis.
4. Our truck and payload worked well where you are going.
Our dimensions were:
- length: 27.17' / 7.98 meters
- height: 12.04' / 3.67 meters
- width: 8.58' / 2.62 meters
- Front axle track: 65.6" / 166.62cm
- outer edge of tire tread - front: 71.75" / 1822.45 mm
- outer edge of tire tread - rear: 79.00" / 2006.60mm
- Turning radius: 28.2' / 8.56 meters
5. Speed means nothing, especially where you are going. 100 kph is flying on those roads, and generally only the chicken bus drivers live in that danger zone. You'll spend most of your time at 40 - 60 kph. That will seem very fast on some of the one lane shelf roads.
6. The ability to filter and sterilize water is important. This greatly extends your time off the grid, before you need to re-provision.
7. You will need the ability to create your own electricity. You will need to power and charge batteries for a wide variety of electronics. A diesel generator in addition to solar panels is a very good idea.
8. You will spend most of your communications time in local internet cafes. For times when you are on-site, you will want to have the ability to communicate via multiple systems. It is very important to have sat comms that utilize different constellations, as you will be in areas where you cannot "see" the satellite you need.
We used:
- Unlocked, quad-band GSM phone with local carrier SIM cards
- Iridium sat phone
- Inmarsat BGAN (broadband)
- Low data rate text & telemetry sat system
We also carried a couple of EPIRBs. I recommend that your field teams be well versed in basic emergency procedures, including how to use the EPIRB.
9. Close-able, lockable storage is a very good idea. As long as you put things away and keep them out of sight you will probably have zero problems with petty theft.
Summary:
For your intended use, I think you would be well served by a two vehicle solution.
A basecamp vehicle can offer the size and dimensions that can provide a shower, hard walls, lots of water capacity, work space(s), electronics, amp hours, indoor kitchen, etc.
A small "scout" vehicle can provide the size and dimensions to get down trails to sites and to run errands back to the nearest panaderia (very, very important where you are going 8^) ).
A Fuso based chassis, 2007 or older, would be a good choice for your basecamp. That chassis is well represented in the countries you are headed. It's popular as a market town freight truck and, as previously mentioned, as a bus chassis. You will see zero 4x4 (FG) models, but most of the parts are interchangeable with FE series, which you will see a lot of. This means that mechanics will know how to work on the chassis and there will be parts available.
A Toyota HiLux diesel 4x4 four-door would make an ideal second vehicle. It can take the entire crew back and forth from the camp to the work site, as well as run errands, scout out sites, etc.
As noted, the village-to-village chicken bus roads are optimized for the Fuso chassis dimensions, e.g. bridge track width, etc. Smaller roads/tracks that are off of the chicken bus routes are optimized for the dimensions of the HiLux.
Bonus:
I collected more than 1,500 South American waypoints while we were there. Some are ours, most are from other overlanders. You may find them useful during your time there.
http://www.hackneys.com/travel/index-gpssawaypoints.htm