Here is the inside of my (home made) plastic chest box. I forgot that the side brackets were mounted on the side walls, and the top mounts to the front wall.
(Yeah, I have had some ideas for putting some kind of LEDs inside, but I have not got very far...)
By the way, here is a tip for making the collar. I have previously posted these pics over on Rebel Legion's msgboard.
I took the existing 3" wide collar from the coveralls, ripped the seams and ironed it flat. Then I divided it into two L-shaped pieces which I made the flight suit's collar from. The only external seams are along the collar's edges and at the precise back of the neck.
The "overlap" is the width of the flap in the front.
And this is the result:
Oh, and be sure to attach the velcro
before sewing it together, or otherwise the seams will be visible, as on CostumeBase's suit. That doesn't look very good.
You could glue the velcro on with a thin layer of fabric glue before stitching - that will help hold it in place and move around as you stitch.