I did a switch swap on a mate's LP Supreme a couple of months ago and there was no shielding in the cavities.

On the subject of Faraday Cages there is a very impressive one at Garden Island in Sydney, it's the navy war room. The roof, walls & floor of the room and the long winding corridor into it are all welded steel and the only penetration for communications is optic fibre.

I don't know if it's still there or been moved it was around 1991 when we did the comms upgrades there, even if it's still there I guess what I installed is long gone because technology has come a long way since then ( but it's still all just zero's and one's )