Thx guys, think i am gonna go with vulkem. Looks like somebody on Amazon is selling it in colors now! Oh, and it's not rigid, it never completely hardens. It's a polyurethane sealant used for campers and such, and it holds my (and many) Airstreams together.
Yes, silver e350, i've seen it spelled both ways, but it appears it is actually Vulkem on the package.
Thanks, i'll post how it turns out.
Also, for those who might ever stumble across this and try this product to seal up something. It is awesome AND possibly the messiest stuff i've ever touched. You will wind up with it EVERYWHERE, and it likes to stay there. Perfect for filling leaks and makes a great wearable accessory for guys days after it's use.
http://www.amazon.com/Black-Tremco-Vulk ... CRGCA4E4N3