Is this what you are talking about?
http://www.homedepot.com/prel80/HDU...&search_text="tough%20box"&DRC=4It might be the same as this:
http://www.contico.com/automotive-foam-wb.htmContico also seems to make other structural foam thingies:
http://www.contico.com/automotive-sub-foam.htmThanks for the tip - I will be looking around.
Jonathan