Plenty on this in the archives, but based on my experience when my '85
was totaled:
1.  Ask to see the comparable sales the adjuster is using,  I my case
they were using Vanagon sales, not Westfalias.  When they corrected this
it increased the settlement amount by about 40%.
2.  Find adds in your local area, but especially look in Autotrader.com.
I did and so did the adjuster.
3.  Get an opinion from the local VW dealer on what he would be asking
for the van if on his used lot.
4.  Produce all your receipts to show what good condition the Westy was
in.
5.  Keep insisting that you want a replacement, not money.  Keep telling
them you want THEM to find the replacement.
6.  If your insurance provides a rental, take it!  Puts a little dollar
incentive on the insurance company.
7.  Be a little patient.  The adjuster has an incentive to get the claim
cleared, it reflects on his performance.

Good Luck