Well not a car build but might be interesting to others. I am in the process of building a welding station that is made out of a 24" x 48" Dewalt job box that was on sale at Home Depot recently.
The plan was to build something like this:
I think it is turning out pretty close.
3/8" thick laser cut top with 91 5/8" holes for clamps/dogs. I step drilled the 6 mounting holes and used tapered head machine bolts to bolt the top on.
It is definitely flat enough for my uses.
The next step is to cut open the side and insert my welder on HD drawer slides. I also have to fab up the shelf on the side for my bottles.