You seem to be talking about several different things. You want to use the stainless tub about 6" x 5" x 1.5". Assuming you would pour your copper to a depth/thickness of one inch, that would be = 15.24 cm x 12.7 cm x 2.54 cm = 491 cubic cm as a mold in which to pour (or melt in a klln) molten copper? Copper has a specific gravity of 8.96, call it 9, meaning it is 9x as heavy as water, 9 * 491.6 cu cm = 4424.5 grams / 453 = 9.76 pounds. Are you saying you have a furnace or torch that can melt 10 lbs of copper? That's a lot of molten metal to be slinging around, that would take a serious load of heat. I guess it could be done in a kiln. Copper needs a controlled atmosphere not to freeze from a melt with a scabby, oxidized finish, and maybe you would or could achieve that in a kiln.
Or are you saying you wish to electrolytically refine copper in the cleaned-up stainless tub, using some sort of cell? I think that might depend on the type of stainless. Iron is more reactive than copper, in fact each of iron, chromium, and nickel are more reactive than copper. IMO you would just have to experiment. Is the stainless going to be one of the electrodes? Or are there two electrodes between which current would flow and the stainless is just the container and not part of the circuit?
It's not at all clear to me what you are trying to do.
