Quote Originally Posted by wilfy View Post
expanding foam is also something i was considering for my build.. it's very cheap and i think it would go some way to take the ring out of the steel as it wouldnt have any air to resonate through the center of the box section
Doesn't work I've tried, it's not dense enough complete waste of money if you do.

By far the best thing is kiln dried sand nothing really comes near for ease of use or cost.