4x4 truck makes more sense... cheaper and less added work for 4x4, plus all the pickups have stiff boxed frames now, making mounting much simpler. Hate the long/tall hoods on the trucks, though...
But, you can get more living space from the van chassis for the same overall length vehicle and you can include the front seats as part of the camper if you design it that way. The truck chassis is a different vehicle. I was just comparing the Transit with the E-350 and true 4x4 options