I would think that instead of big with a gas guzzling engine you might go for something more like the old Willys Jeep. Fairly small, compact, with a small, simple, fuel efficient engine that carries a lot of weight for its size through gearing. The old Jeep only had, depending on year, about between 20 and 60HP worth of gasoline engine with the majority or wartime production having 60HP. At capacity, considerably more than 3/4 ton, on a flat road it would only do 40 mph but, as the saying goes, it could climb a tree.