your right there is a way to add a piece of 1/4" thick angle accross between the frame rails...thats how I built mine...
I made my own conceled hitch back in 2000
I used a way beefier design than what is pictured above, however I abuse mine...bigtime...
I have towed almost 15,000 lbs like 200 miles (zero tongue weight)
Yarded 17,000 Board feet of Huge logs with it and pulled out countless over-egoed 4WDers....
So mouch abuse in fact that my pin-hole in the receiver, now looks like an egg-shape...
Anyway, with a little more "beef" to the above design, it should be able to handle heaver loads and or winching....