I'm sure the feed to the Boot light switch is permanent live (up near the petrol filler), and an ignition live would be one of the ones in the Window control box - maybe. (I'm very helpful aren't I ))
You can get both these from the back of the fuse panel. It was fairly obvious which the main feed was and a few min testing with a meter found a switched live. You can easily route cable from there either up and out across the top of the tank or out by the rear light cluster.