I plan to install electrical outlet in the following location:

[![enter image description here][1]][1]

It would be used mostly for:

1. USB camera that is always plugged in.
2. pressure washer. 
3. car charging.

I plan to splice the wires from the electrical box behind the lamp:

[![enter image description here][2]][2]


I watched few youtube videos on how similar projects are done and If I understand correctly, I have to:

0. Turn off electricity at breaker box.
1. Buy [old-work electrical box][3] (i.e. one that has those wings and can be attached to the wall opposed to stud). PVC material should be preferred as then I don't have to use metal-sheathed cable.
2. I need to drill a hole in the wall where the new electrical box will be installed and then use a sawzall (or something similar) to cut out rectangular shape that matches the electrical box.
3. Punch a hole in the bottom of electrical box behind the lamp. Punch a hole in the top of electrical box that I just bought. Guide the cable behind the wall.
4. Buy a [15 Amp GFCI protected outlet][4] because GFCI is mandatory for outdoor outlets. Connect all 3 wires to it and screw in to electrical box. Splice all 3 wires to the lamp wiring in it electrical box.
5. Buy a Plastic [Weatherproof in use cover][5] and attach it to electrical box. In-use is mandatory as I would leave camera plugged in at all times.


**Am I missing something? Do I need wire clamps too that would lock wire in the electrical box? Do I need to apply silicone caulk somewhere? Is it ok to install outlet that high from ground? Are parts that I plan to order compatible with each other? Do I need to check wiring going from light switch to the lamp if it can handle 15Amps?**


  [1]: https://i.sstatic.net/JozBE.jpg
  [2]: https://i.sstatic.net/ctwae.jpg
  [3]: https://www.homedepot.com/p/Carlon-1-Gang-14-cu-in-Old-Work-PVC-Electrical-Outlet-Box-B114RB/100404027
  [4]: https://www.homedepot.com/p/Leviton-15-Amp-Self-Test-SmartlockPro-Slim-Duplex-GFCI-Outlet-White-R02-GFNT1-0KW/206001533
  [5]: https://www.homedepot.com/p/TAYMAC-1-Gang-16-in-1-2-3-4-in-D-Weatherproof-In-Use-Cover-Clear-MM420C/302216014