Have used Berker Sockets on previous boats and just bought for new to us 36c. Back box should be used but if the existing one is Berker just reuse.
If using one of the 12v or usb sockets then back box less relevant as long as the wiring is suitably supported.
If getting the sprung covers as well bear in mind that they can get n the way if you have plugs with wires exiting the “wrong” way or plug usb chargers etc into the 12 sockets