Yes, the entire top seam was welded continuously, then ground smooth on the outside only for cosmetic purposes. The rest was stitched inside and outside of the panels as you can see in the pics.
The slides are 250mm (9.84") Fulterer 5000 series drawer slides.
They have some kind of free CAD program there, not sure how good it is. A set of dimensional drawings would probably suffice for something simple like this, and they could do Al for weight savings.
I'm not shilling, I just remembered them because they build the sheet metal parts backblaze storage pods.