I posted this picture before and a keen eye would have caught the electrical in the shed. When I added the shed on, I wanted an outlet and a light, nothing fancy, just access to some power for outside if need be. I didn't want to run two runs of Romex (NM) for each so I ran power to the outlet than to the light. I'm not too worried about tripping the breaker and losing my light at night.
Once I moved the trailer, I "needed" power to plug the trailer in while it's at home. So, my thoughts were to tie into that box and bring some power out. Not wanting to completely stuff that box full of wire and then try to push a receptacle into it, I decided to add another box for a junction box.
First order of business, was to remove and replace the receptacle with a GFCI. Then peel some siding off and mark for the holes. One in the siding for the mounting box and another through the wall.
Adding the GFCI in the shed should protect both the outlet in the shed and the one outside. I mounted the block and box, wired in the receptacle and finished replacing the siding/trim.