Yes sir, Ron. I have a 12v outlet in my trunk wired directly to the battery. It is " hot" all the time. I do use it to run my air compressor when needed. Charging a phone is one thing ; running a compressor is another. The versatility of wiring it directly to the battery with a 15 amp in-line fuse is the best option that allows for multiple functions.As far as I know both Budoka and Chopin114 are correct. The reason you might not want to plug directly into the pigtail (assuming the '12 still have it) underneath the trunk lid is that it is probably only 3-5 amps like the pigtail in the left front pocket. If you wanted to plug something like a small air compressor into it you may fry the circuit. I mounted one in the designated space in the trunk but ran straight to the battery and put a 15A fuse in the positive lead. I use the one in the left front for cell phone, etc.
I apologize for repeating what has already been said by Budoka and Chopin114 but just wanted you to understand why you might not want to use the plug & play pigtail that is already in the trunk.