Armor hidden door ideas?

this is the back of the halo 5 recon shoulder piece i didn't build the strap piece because I'm going to add a nylon strap to hold it in place i want to close up the back but also want LEDs in it is there a technique anyone knows to make a trap door? are like a hinge? so i could close up the hole but open anytime?

I did something similar with the drum mag on my SAW. Mine was eva, but you could easily transfer the idea to pep.I recessed a slot into one side that the false panel slips into(you could substitute the slot and groove for a hinge that you epoxy to your finished product), and then I embedded two rare earth magnets into the opposite side of the false panel and body of the drum mag that keep it secure.

Edit:
As far as finding a hinge to use, check your local home depot or hardware store. They generally have lots of small hinges you can choose from. When you go to epoxy your hinge to the finished part, be sure to rough up the steel of the mating surface with a Dremel, file, low grit sand paper, etc. In order to ensure a strong bond.

That's a good idea, not to difficult either

Magnets are great, I use hidden compartments to keep my batteries and wiring hidden.