Two suggestions - keep it light to keep your van light and keep it
sealed to prevent it from holding water.

I have found the sound proofing works well, when traveling at 55 mph or
less, otherwise wind noise overtakes everything.

I have a lot of extra butyl mat if someone would like to purchase it.
pmail me.

Dana
85 Westy 1.9td
04 Beetle 1.9tdi