Easier way to do it...
1. Go to home depot and buy a couple of weatherproof rubber sockets (Pic 1). Also get a piece of sheet metal cut to whatever size you will need and some socket splitters (Pic 2). You may also need some glue or some liquid nails also works. Pic up some wire while you are there. Make sure that it is rated for up to whatever wattage you are going to be pulling in the end.

In the end you should have something that looks like pics 3,4,5. Only with 2 more sides to it.