I've owned 6 full sized vans, 3 Chevys and 3 Dodges.  I bought 3 of them new
and 3 of them slightly used.  They've all done that.  The last 2 have been
Dodges.  I own a 2002 Ram Wagon 3500 right now.  I just accept the outside
tire wear on the front and rotate tires, etc to compensate for it.  I have
even gone to a tire shop, had them remove the tires, flop them over, put
them back on and swap sides L to R and R to L.  That way, the worn part of
the tire is on the inside and the tire is still turning the same way.
But that's just me.

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"Lurker"  wrote :

Your Van is likely not out of alignment. This wear is common when there is
such a weight loading on the front. Sometime try to observe the front tires
from the side of the road when your van is going around corners. You will
notice the tire trying to roll out from under the wheel, which severly
stresses the outer edge. The only relief you have is to go to an "E" rated 8
ply or more truck tire, if you have not already. These vans require
extremely stiff sidewalls.
Steve

I've checked and set the toe-in on my '70 Blazer for all the years I've
owned it (27), with a tape measure and a sliding set of tubes (a couple of
old tent poles).  Something similar would work as long as you can accurately
measure the distance between the same parts of the rim on the back side vs.
the front side.  Without knowing your specs, probably a 1/16" difference
(larger on the rear) would give you all the toe-in you need.  The toe-in is
the spec that most frequently gets "out".  Too much (1/4" for example) will
cause excessive wear on the tires' outer edges, too little, or toe-out, will
cause wear on the tire inner edges and could be dangerous causing the
vehicle to "wander" or pull from one side to the other over any little bump
in the road.
LD