RE: Correct tire pressure
I've also used another method to double check my tire inflation, a
small infrared remote reading thermometer from Radio Shack.  The first
rest stop I pull into (or gas stop) on a trip I check the temperature
of each tire.  I'm going on the assumption that if they are all
running a close to the same temperature that I'm inflated properly for
the load distribution.  On one run I deliberately lowered the pressure
on the rear tires 5 lbs before taking off, check at a rest stop about
40 miles down the road.  The rears were running about 10 degrees
hotter than the fronts.  I hauled out the 12v compressor and aired
them up to where I normally run and the next check showed them all
within a 5 degree range.
One caution on this method.  If you are running for some distance with
hot Sun on just one side of the van you will find that the tires on
the sunny side will be several gegrees hotter than the shaded side.