RE: Vanagon Traction
I had a similar experience last Spring, on the level but very wet
grass/mud.  I'm running Michelin Agilis tires and that was the first time
they had ever disappointed me.  At that event we towed a bunch of Vanagons
out of the wet grass and watched a bunch of Buses drive out without
difficulty.  All in the weight, weight distribution, and tires.