Stephen Stewart wrote the original draft of this document in May 2007 as he returned to Europe on a Grimaldi RORO ferry. He spent the previous 16 months in Central and South America, driving and camping in his custom Unimog camper. Prior to that trip, Stephen drove to China on a year-long trip, and to Siberia on a 7-month trip. I think it's fair to say Stephen knows a thing or three about overland travel.
It's also worth mentioning that Stephen's recommendations are for vehicles where the living quarters are inside the vehicle, not beside it. So vehicles suitable for towing a caravan or camping with a rooftop tent (e.g., Land Cruisers and Geländewagens) are not discussed.