Any insulation in that area or any area on a vehicle can trap moisture.
Moisture is trapped when I has nowhere to vent to an area of less moisture.
Then depending on circumstances in that area may condense to form liquid.
The same is true about the internal of many other closed panel areas.  Many
of these areas are also filled with the same insulation.  When I pulled the
stuff out of the cab roof I found corrosion around the adhesive used to hold
the insulation up.  None of it serious though.
jimt

On 5/17/05 11:48 AM, "Christopher Gronski" <gronski@GMAIL.COM> wrote:

> I'd stay away from any insulation that can trap moisture (including
> the stock fiberglass stuff) that is why our vans rust so bad back
> there...
>
> Chris
>