Sew inside rectangle

[LtMac]

Hi!

Long time lurker here. 

I am trying to make a useful radio holster using what I have learned over the years as a user 

I need to sew a seam inside the holster as shown in my photo.

Any thoughts?

Dimensions are 2 3/4 inches x 1 3/4 inch and about 3 inches deep.

Edited April 2 by LtMac
add dimensions

[Mablung]

Is this one whole piece of leather that you have sewn into the box shape? Are you trying to sew another piece into the bottom of the holster? Is this seam meant to be hidden in the back or go all the way through the front? Pinch the front and back together, or be decorative, or attach another piece somehow?

Some more details of what exactly you’re trying to accomplish would be helpful. 

[LtMac]

This is one piece. 

Seam may be hidden or seen, it is to keep the seam where the box comes together up the back from coming apart - to add strength where there is none. 

[LtMac]

The red line needs to be circumfrential to add stability, strength and longevity to the piece. It is intended to go into fires, keep the radio in place, where a firefighter can get to it with muscle memory. 

[AlZilla]

Is the back and the front one continuous piece? And the sides start out as sort of flaps that wrap around to the back?

Maybe a picture of the other side would clarify the challenge.

EDIT: "This is one piece" means the pattern is a single piece? Not that it's one of a given number you need to make?

Edited April 3 by AlZilla

[Mablung]

I think we’re still missing some important design details here. It sounds to me as though you’re saying you want to add a line of stitching around the whole piece, including across the back, to add some additional dimensional stability. The leather itself will likely do that on its own without punching holes through it and putting thread through it. In saying that, I’m assuming the front and sides are one single layer and you have one whole piece of leather with tabs cut that fold to the back, where all layers are sewn together, as AlZilla alluded to. I’m also assuming you’re using a reasonably heavy, thick weight of veg tan. If my assumptions and inferences are right, then all you really need to do, it would seem, is add an additional seam to the back, where you’re already sewing it, or double-stitch the existing seams. 
 

Am I missing something here?

ETA: Some additional pictures, at minimum of the back, would be helpful, too. 

Edited April 3 by Mablung