I have a 2WD 85 Vanagon that I have taken off-road many times.  It has plenty
of clearance for most stuff.  I used regular Mud and Snow tires, but that was
usually in dry stuff.  Never really got stuck.  Stock suspension with
original shocks (!) bounced over everything.  Fire roads, Jeep roads,
riverbeds, arroyos, high desert, no problems.

The most important thing to remember when preparing the van for off-roading
is:
DON'T LEAVE ANY LOOSE STUFF LYING AROUND!!!

And put your tool box under the back seat, or inertia and gravity will spread
all your tools all over the van.

Bill Marshall
'85 GL Tiico "Pandora"
Aurora, IL