Hello,I recently did my 85 westy w/soundproofing.I researched the list and
used most of the products/tricks that I found.I can say that the most
immportiant single ingredient for good sound proofing is  a good set of
QUIET  tires.All my work and expense was mostly for not without these.Next
on the list,is to  put most of your product on the floors.Dosent seem to
matter what product you use,but do be concerned about any vapors that are
released.I used r-Blox 100 sq ft(got it on ebay-like dynamat).The produce
for speakers from Parts express that was used on the list(3 large
sheets).dKool seal in the wheel wells(3 gallons).4 by 8 foot sheet of 1/2
inch thick neoprene rubber on the fiberglass roof.I got the factory
soundproofing from a dodge caravan ,rear floor area(2 5 by 6 sheets.This is
a tar like substance bonded to felt-rag).I used dynamat extreme on the a/c
($90-wow)This sheet was used to wrap the unit.I use r-blox on the front
radiater fan schroud.These,plus a few other items are what I did.Tires are
the best improvement.