Personally, I just mounted a vise to a square of plywood which I can then clamp to.....whatever.
Additionally, I picked up one of thos cheap suction cup vises....it sticks well enough that in conjunction with a mag well block, I can do a lot of work on a build without hauling up a heavier vice from the basement.
Works well for me.....and lets me work in the kitchen or the shop. I'll try to post some pics later.
ETA: OK, here are some pics. I was too lazy to clamp up the big vise (I just threw it up on a bench in the workshop)....but I just clamp it to the edge of the table using two clamps...corner-to-corner, so to speak. It's perfectly stable for changing barrels or whatever. Also, while not specifically what you asked for, I'll include a pic of one of the Plastix-Plus stands. It's a nice accessory....