I made one that is sort of like tool #1 out of scrap I had laying around.
I think the base was some 2" square tube 1/2" all thread as the post.
The top is also square tubing, maybe 1-1/4" or 1-1/2"? with a hole on each end, then some round tubes (to press the retainer down) that were put into the holes of the square tube and welded so they can't move. The footprint of the tubes pressing on the retainer is fairly small, like what would happen with "C" clamps, but worked that way. I "improved" it by welding some curved pipe sections to the tubes.


Large "C" clamps will work too, but you need a flat plate on the bottom