This is what Demon said to me in a PM:
"I just used a good industrial expanding foam sealant from Home Depot.
This stuff was very thick to begin with. High pressure exanding urethane.
It definitely firmed up the unibody. I noticed it right away.
It also brings with it a bit more vibration, but IMO that's a minor trade off.
Some may say it just gives a better 'Road Feel'"
Not having checked on prices, I can't say for sure how much cheaper the HD stuff is, but at least with the Foamseal stuff, you know you have the right foam, and the guesswork is gone. It's the same stuff spec'd by Ford for the Mustang, as well as by Lexus and Infiniti for various cars.
And, if you get the wrong stuff, there is no going back
