The Germans call this the magical formula “623”:  6m long x 2m wide x 3m high.  I personally prefer to keep the height down to about 2.5m with the use of a pop-top tent because you are less likely to get hung up on trees, or rock outcroppings, and you still have a shot a fitting inside a shipping container, in the extreme case by switching the wheels to “low-profile container wheels”.  There will be some trails where this class will be too wide to fit because 2m is wider than a Toyota Hilux, Toyota Landcruiser 70 Series or Ford Ranger, which represent some of the most popular vehicles for remote travel in many parts of the world.  This tends to be more common in Africa and Asia than the Americas, where US full-size pickups are common, and these vehicles are 2m wide.  Overall, this is a great vehicle category that is still very capable and can reach almost any destination while allowing for a bit more creature comfort than the previous categories, especially for families with a couple of kids and possibly at pet that travels along.

Examples:  US full size pick-up trucks, US full size vans, Iveco Daily 4x4 truck or van, Bucher Duro 4x4 & 6x6,

Please note that the popular Unimog Model 1300 (and up) does not fit in this category!  While representing one of the most capable off-road vehicles in the world, they are 2.35m wide which makes them too wide for many narrow shelf roads in mountainous terrain.  These later models are also quite heavy because they are setup to carry heavy loads and accept many bolt-on accessories for construction, forest or fire service and agriculture.