I have tried several different approaches to tires, with mixed results.
My 87 came with a set of Continentals, 6 or 8 ply rated.  My second set
was also a set of Contis, different tread pattern, slightly higher load
rating.
Had a tread separation, and swore off Contis...Then the fun began.
The local tire store gave me the same story about the "special vanagon tires",
made only by Michelin with reinforced sidewalls, etc.  OK, says I, order them.
I got a pair of MXL 185Rs; these had a maximum pressure of 40 psi, a lower
load rating than either of the sets of Contis, lower ply rating, etc.  They
also
wore out pretty darn fast.  Since then, I have been using whatever LT rated
tire Price Club/Costco has available.  ( Uniroyals twice, Kirklands once ).
I think that the load rating and ply count are more important than the
magic reinforced sidewalls.  I also found it hard to believe that a tire
which could not take the recommended 48 psi for the rear could be the only
right one for my van....

        Just my 2 cents ( or less ! ) worth...
        Chris
        87 Wolfie