Truth,
I chose the felt because of the 72" width (and the $4.99/yard price tag) where most fabrics are 56". This particular design requires at least 58". If you can score the burlap in 72"...go for it!
Glen,
Thanks for your expert opinion! Knowing that objects transfer low energy better than air, I was afraid of that. I guess I rationalized the 1 1/2" + 1 1/2" (3") would not be as much of a factor, but that was a guess at best!
Divine,
Great link, isn't it? My $29 cost was including shipping, fabric, lumber and an open back design. The ATS at 48x24x4, open back and shipped at $69 are still a steal!