If you don't have access to air tools (like me), here's what I've done in
the past. I had to jack up the wheel I'm trying to get the nut off of about
an inch off the ground,  put the socket over the nut (make sure you remove
the cotter pin), and set the bottom end of the 24 inch breaker bar on the
ground. Then put bricks both in front of and behind the other three wheels.
Depending on which side of the van you are on, and which way the nut needs
to turn, I start the van, and put it in either first or reverse. Slowly
take your foot off the brake and the differential will cause the wheel off
the ground to want to spin (you will want the wheel to spin in the opposite
direction you want the nut to turn) , but the breaker bar and the socket
will want to hold the nut still. Viola! Off comes the nut.
Here's the disclaimer so you can't sue me: CAUTION! THIS PROCEDURE CAN
CAUSE BODILY HARM OR DEATH AND CAN ALSO DENT YOUR VAN OR BREAK OTHER STUFF
IN YOUR GARAGE!
Never had any problems myself, but be aware that it's putting a LOT of
stress on that breaker bar.
YMMV. Good luck.
Joel