Im with Ulti...
I used to shield pup cavities but now days i dont bother as most pups are wax potted and shielded anyways..
For long cable runs i use shielded cables as it is the cabling that will give rise to most RF interference.
In short, shield your control cavity and cavity cover, making sure you have contact between them.
Also, a dab of solder on the joins will ensure good conductivity.
The other great thing about shielding the control is you wont need to run an earth wire between the pots as they will earth out on the shielding
And you can get your shielding tape and cabling from us here at Pit Bull for a very reasonable price..