between the skin and the crash bars which served the same purpose as your butyl rope. IMO anything that functions to bond or attach the two crash bars to the inner doorskin is going to produce similar results. But, simply mass loading the doorskin with something like Dynamat still leaves a lot to be gained. It is not enough; The major elements of the door structure need to be unified as a single entity. After that, all that's left is to focus on cable rattles, lose wiring connectors, etc.
