Cool never thought of closed cell would be a real difference.I actually am using fatmat with closed cell foam under the vinyl for the trunk.The way it is done is fatmat,trunk carpet,with .5 inch mdf wraped in heavy dense foam then foam backed vinyl.So use foam on the doors (closed cell)on top of fatmat.I will be building a box to fit in the trunk going to try fiberglass.The wife just bought the box cause she wanted to help with the install she did 90 percent of it by herself pretty cool.She can do tune ups plugs oil tires and cook a mean steak.lol Sould I post pics of the build or am I to new still reading the rules.