I made this by building a rough dam out of plastic bags and filling it with A-B Urethane expando foam. (BTW, the spray can variety won't work.) You gotta make sure none of this mix gets on the plane cuz it is one really fantastic glue; it'll take the paint off. Anyway, I pulled the foam off, sanded it to shape, and glassed it. Then I dug out most of the foam and added some glass/epoxy hardpoints for mounting.
Does it do anything? I like to think so, but can't notice any difference in performance.