I went to the gun show yesterday, mostly looking for one guy who used to sell old lenses. Either he wasn't there or didn't bring any lenses (I think it was the latter).
So, having bought nothing, photography or gun related, and having nothing else to do before work, I remembered my need for something like a heavy cutting board for a base, and went to Bed, Bath & Beyond.
Lo and behold, they had quite a heavy cutting board of an appropriate size and thickness, and for $40 instead of $75.
I'll probably drill a hole for a threaded insert and move the furniture foot to it today.
The t-rails on which I mount my flashes are too long for the cutting board (18" long), so I took an extra 24" rail and cut it in half.
I still have to mount the 5/16" threaded insert.