I'm in the "one mounted at a time" category because my bench is a shelf the width of an "under the stairs" closet.
Wandering around my local steel supply store I found these 6x6x1/4" plates with a 1/2" hole in each corner.
They were $4 each so I bought a bunch to bolt under all my presses to standardize the press/bench bolt pattern.
I mounted the presses kitty-corner to get the center/rear bench bolt furthest away from the press to minimize rocking.
I didn't tap the press pattern holes in the plates but used T-nuts instead.
For the Lee presses I had to cut the plate corner back further and weld on a wider strip because the side mounting holes were further apart.
The hand knob/bolt on the Loadmaster is because the press is on the storage shelf, not the bench.
That other pic is most of the presses on the storage shelf.
I have 3 all-thread studs mounted in the bench and use coupling nuts to bolt the presses down.
These plates have proved to be rock solid under all presses.
works for me,