Tire size and tread design are related and must be balanced for optimal performance. For a heavy vehicle like a camper van, I say skinny is better than wide. Wider tires provide more flotation but a heavy van will never benefit from that like a Suzuki Samurai or other lightweight rig will. A good test is loading to your normal weight and driving your typical terrain. Stop in a traction-sensitive spot like on a hill or in mud and try to take off pretty aggressively. If the tires spin but do not propel you forward, (like just floating on top or bouncing) go to a narrower or more aggressive tread. If they bite and go with no spin, you're golden. If they spin and sink (rather than float or bounce), go wider or less aggressive.
My heavy 2wd van has HT tires and will spin and float rather than dig. A wider tire would help (less prone to spin) but not as much as something more aggressive (which would dig and go), but something more aggressive (MT, AT, etc) would impact the highway driving characteristics more than a wider tire would and they'd wear faster, etc. This not a good example I guess because my van is 2wd and doesn't get off the road much.
My 4wd truck has aggressive ATs (Duratrac) and is just about perfect for its weight and use (just hunting, working on the farm, etc). If it was heavier a less aggressive tire would work as well with less tendency to dig. If it was lighter, I'd need an MT to get the same performance I get now from ATs.
For good driving characteristics in a multi-purpose vehicle, I say go as skinny and mild as possible, but as wide and aggressive as necessary.
