I need to try that...my sub is too close to the turntable/rack resulting in horrible feedback. I can't use the sub with the turntable....
Since CF, put in a new audio rack and bought a bigger sub.
http://www.definitivetech.com/Products/products.aspx?path=Subwoofers&productid=SuperCube%20Reference . I made a place for the sub right under one side of the new rack. It has no effect on my TT. According to Rega, TTs need complete isolation, and they sell a wall mount to help accomplish that.
My system sits on a concrete floor. The thick Sorbothane completely isolates components from all but room vibrations created as I dance naked and sing too loudly.
The thick stuff is made for home construction in earthquake areas. You can find it on Amazon. It really tames a sub, or isolates any component. It looks kinda expensive until you try it. I buy the sheets and cut them into 1 inch squares. Here on the deck, it keeps my Polk MicroPro 4000 from ripping the deck from the house.
As to feedback, subs are prone to that. Run a separate power line if you have a big one.