So I got a stewmac version of a guitar repair/gunstock vise today and plan on adding it to my bench (I neither repair guitars nor gunstocks - just a handy vise). I don't really want to clutter up the bench permanently, so I came up with a plan and figured I'd share in case anyone has a similar conundrum. I also have a machinists vise, saw vise, and common shop vise that I would like to leverage the stability of my bench while using.
I am going to get a hitch receiver tube and have it welded to a plate that is lag screwed under the table (you can see where this is going). Each vise will have a plate welded to a 2" drawbar at the appropriate height. Bolt on the vise. Any wiggle is removed by tapping a couple of 3/8" bolt holes on the side and bottom of the receiver to run up against the inserted square tubing.
Pre-fab receiver and bars can be gotten at any trailer supply unfinished for welding. If you don't have a welder, these are simple and cheap for a shop/friend to do.
For off-use storage, I can just put a few 2 x 2 holes in a block of wood mounted to the wall for handy access to the vises. Or, I can just put them in a cluttered heap in some corner (more likely).
If anyone has a better idea, I am game.