Permanent live shouldn't be a problem as the battery is in the boot.
Switched ignition might be a bit more tricky as the sub is passive to the best of my knowledge so the only connectors will be the audio connections from the amp. The only other thing I can think of back there is the AYC pump but again that's only energised by the ECU when it's needed to the best of my knowledge so it isn't powered the whole time the ignition is on.