Here's the way I did mine, I made a box made of sintra or sign plastic, snug enough to fit the exact size for the chest display. I measured the sizes in all angles so I came out with this, specially thinking in waterproofing the chest display, and at the same time as comfortable as possible to fit under your vest.
measuring the right fit of the display, that doesn't wiggle inside the box, which I managed to add a little strip of plastic for a tight fit, which you could add inside in the upper or lower part,
And making sure that it fits with the right angles based on the curves on the armor, which most likely you want to trim a little bit the areas where the box connects to the armor. Remember to keep in mind that it has to be fit and close to the armor, making sure that the display is aligned correctly inside and that it work properly from the outside, then hot melt glued to the armor for sealing the box in the areas between the white box and the armor, not touching the brass contacts or the circuit board inside, which should be free of obstacles for the ribbon cable to fit, and avoid damaging the whole system.
Hope this helps as an example for everyone. All you need is a little patience with this, not all armor are made the same, including the fact that there's the dark film inside the slots for the effect, besides to protect the display from water and other elements, specially kids sneezing in your armor (or sort of...maybe someone could puke drunk in your armor at a party
)...but you get the idea. Planning to install an on/off switch between the battery adapter and the other circuit board, which will be resting in a pocket inside the vest facing your body, and the switch to place it somewhwere accessible. Any questions, just ask me.
Robert