I guess I think a little differently,I lived in a 4x4 truck for 4 years and never got stuck once although I've been on some BAD "roads"!! In the last year I've gotten the van stuck 6 times. So now I have the most aggressive mud tires I could find on the back of my van and will probably put a locker in the axle and add a winch.
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This may seem a little off the wall, Bob, but there's one other option you might think about . . .
You could fit a junkyard transfer case to your van between the transmission and rear differential. In difficult terrain, you drop it down into 4LO. The front yoke would spin harmlessly. The torque sent to the rear diff would be multiplied the same as on a 4x4.
Regards
John