I had very good luck, with my last 2 vans, using fatmat.  I"ve got some
pics and notes on my website out at
www.weidefamily.net/vanagon
browse to Interior
<http://www.weidefamily.net/vanagon/HTML/07/01/slideshow.html> > Insulation

I tried a few different products and ended up using fatmat and was very
pleased. Back then their 100 sf bulk pack (enough to do most of your van)
was just over 100 bucks but i seen it's gone up a lot.
http://www.fatmat.com/shop/fatmat-no-logo-bulk-packs-26000

Suggested tips:  Scrub down your interior van panels with TSP and allow to
fully dry before applying.  Applying in warm weather makes the job much
easier.  When doing door panels cut the sheet into 1 foot square pieces and
approach the job like a patchwork.  Trying to get a custom cut sheet into
those door panels is a real hassle and will leave you with little to no
skin on your knuckles.  Some areas of the doors had a leftover waxy residue
which vw had sprayed to prevent corrosion.  You can assist the adhesion of
the fat mat by washing and then applying some contact cement before
applying the sheet.  Get as far as you possible can up behind the
dashboard.  A lot noise comes from the front of the van where the wind
slams into it at speed.  Doing the seat podiums up front will make a huge
difference.

all the best with your project,
Brent

--
Brent Weide
Portland, Oregon
www.weidefamily.net/vanagon/