Here are some images to explain how the large side panel works. As you can see, the side panel has a pocket at the top (with top stitching in the middle), a cargo pocket, and a top stitched seam running down the middle front and middle back of the leg.
This is a simplified version of the construction. As you can see, it’s fairly straight forward once you visualise the design in 2D.
Here’s the version I made in more detail. To create this pattern, I started with a commercial jeans pattern and re-drafted the back leg to have a seam down the middle, then moved the pocket placement to the back seam and re-drafted the front panel to have a seam running down the front. I also squared off the top stitching on the fly front to make it look more like the Fallout 3 design. Next time I think I’ll extend the crotch down a bit further and elongate the fly front to bring my design closer to the 50’s work clothes I found during my research.
Another tip is to wash your denim in warm water and pre iron it before you start cutting out the pattern pieces. My fabric shrank a bit too much during the construction process and I ended up with a snug pair of pants. You can see that the tester garment had a good fit, but I overlooked pre-shrinking the fabric and ended up with a finished garment that was a bit tighter.
The next vault suit will have more ease around the hips and thighs. I’ll also re-draft the pocket to have side panels as the patch pocket added bulk without being an obvious pocket. This gave the illusion of thicker thighs (not good!).