The drawbar is 3" x 4.10 bar channel which is fairly strong and rigid stuff. It's the same stuff I use on when I build clamp-on pallet forks. It's good for taking loads on the top and the sides but not from the bottom, which would happen if you are backing up (it would tend to bow up from the bottom).
The hitch on the end is only welded on the end of the tab and will probably fail sooner than later. I think we have already seen one failure there.
On construction, I would not have used 2" x 1/4" angle for the h-frame but would have went with 2.5" x 1/4" or used the 3" x 4.10 bar channel. What I don't like is the cross members for the bed. They are 1.5" x 3/16" angle sitting with the edge up. I would have gone with 1/4" and the flat side up. However, they did use 3" x 4.10 bar channel for the long members on the bed.
What gives these units their weight rating is the axles, the wheels, and the bottom frame design (h-frame). The Kory has smaller wheels but slightly larger axles but uses a weaker x-frame design to get their 3000 lb rating as opposed the the Country Mfg's 4000 lb rating.
From my perspective, for the price you cannot build one cheaper. What you can do is make a few minor mods and make these wagons real workhorses. They were not designed, nor are they marketed as substitutes for full blown construction dump wagons. These are light estate wagons and should be treated as such.
