I weld on the concrete, being careful to keep the intense heat off of the actual concrete. My knees are always landing on dingleberries and sore from the hard ground. A table like that would be great.
When I was a kid I accidently let my OA torch flame touch my concrete garage floor. A lesson learned, concrete can kill you as easy as a gun when it pops a crater 1 inch and a half round and about one half inch deep. Almost had to change my shorts. This was one fact that I was never taught in Farm Shop Class.
You could mount a propane burner under that grate and char up a nice steak for lunch. Great idea you had and with the price of "new" steel a bargain too. Just another TBN project to put on my list.